Structure-wise, probably House of Leaves. It uses appendices and several categories of footnotes extensively, to the point that the footnotes begin to dominate the pages (putting it lightly). There's so much flipping back and forth that an onlooker would assume you're reading a choose-your-own-adventure book.

Content-wise, it's hard to choose. I'll say The Illuminatus Trilogy, which is a semi-absurdist study of authority and human nature, through the lens of a labyrinthine web of conspiracy theories, jumping between at least a dozen character perspectives.

Godel, Escher, Bach: An Eternal Golden Braid

Blood Meridian (McCarthy) is the only book I finished, turned to the first page and read again immediately because I didn't feel like I got it the first time.

Confederacy of Dunces (Toole) has some of the most unique characters I've ever read. The story of how it got published and won a Pulitzer is almost as crazy as the plot.

There is no Antimemetics division (qntm) is rather derivative of the "SCP Foundation" weblore, but it drills down so hard on the idea of creatures that consume, steal, or are powered by human memory that the plot will bend your mind and delight your imagination. Best science fiction I read in forever.

Last year I read "The Fifth Season" by NK Jemison. It's a trilogy, but this is the name if the first book. Very interesting story, very weird and kind of depressing. However, what makes me suggest it here is that it's written in second person, so it's like the reader is the main character and the narrator is telling you your own story that you forgot. "You picked up your things and went out the door." I've never read a novel written that way before and it was really cool.

House of Leaves

Embassytown by China Mieville, absolutely incredible, almost everything about it is unique. He’s become one of my favorite authors and everything I’ve read by him is original in concept. Embassytown takes the cake though. The aliens are so strange, it’s the most alien feeling I’ve ever had. My brain and thinking is still affected by what I read over a year ago.

Blindsight by Peter Watts is also great with original concepts and delivery.

Easily house of leaves. I've never seen another book play with formatting like that. It has you reading upside down, backwards, all over the place.

Slaughterhouse Five deserves a mention.

Not a book but a comic. I remember being incredibly down that summer and getting recommended Zot! by Scott McCloud and it up my mood. I think that it’s one of the best comic ever written

Always Coming Home by Ursula K Le Guin. It is a fictional ethnography written from the far future about a culture in the near future after life after some apocalyptic event in the very near future. Maybe 1/6th of it is like a traditional narrative about a girl who grows up stuck between two cultures. Her mother is a member of the Kesh which is the culture the book studies and her father is of a different culture called the Condor. Their cultures are dramatically different. The Kesh are anarchic, egalitarian, matriarchal and peaceful. The Condor are capitalist, patriarchal and war like. The rest of the book goes into detail about the Kesh. It tells some of their legends, fairy tales. It describes their performance art. It describes their creation myth. It talks about their holidays and their relationships.

Le Guin is my favorite author ever. The Dispossessed and the Left Hand of Darkness are such incredible books. Le Guin is a very strong anarchist and she uses this book and many of her other works to criticize capitalism. But none of them do so in a way as unique and artistic as Always Coming Home. It's moving, it's touching. It really takes you to another world and culture and helps you to see some of the assumptions you have just because you live in this world. This book is a work of absolute genius. I don't think any other work of art I've ever read has really conveyed something ideological as so personal and moving.

It's a slow burn and parts of it will baffle and confuse you. But the totality of it is so incredibly unique and artistic that I think it's worth suffering through the rougher edges.

House or Leaves for the reasons already mentioned by others.

City of Saints and Madmen by Jeff VanderMeer. It's not exactly a story but a collection of artifacts: some short stories, poems, comics, an encyclopedia full of footnotes etc. that come together to build a world. Some of it is hard to read but the end result is worth it.

Changing Planes by Ursula K. Le Guin. Again a collection instead of a story. In each chapter a different world is described with its people and culture. And Le Guin is great at building worlds. I found this format very relaxing to read.

Discworld series by Terry Pratchett. I haven't read all books (there's too many of them) but if you like satire through fiction you'll find a lot of it here on a variety of topics.

And I think I'll stop here before this becomes a huge list.

Flowers for Algernon.

Dirk Gently's Holistic Detective Agency by Douglas Adams.

You know how usually the first thirdish of a detective novel is all the little clues, the middle thirdish is the adventure + a few more clues then like the last thirdish they have the fight scenes or whatever and solve it?

The first 95% was just gathering random clues. Like in a difficult to follow and almost absurdist way. I had to brute force my attention all the way through but did so because Douglas Adams is one of my favorites.

In the last 5% or so every single one of those random absurdist bullshit clues snapped together perfectly.

Self-Reference Engine by Toh Enjoe takes the most unique approach to story structure of anything I've ever read.

Dictionary of the Khazars by Milorad Pavić.

It’s a novel written in the form of three (Christian, Jewish, and Muslim) interwoven but mutually-contradictory encyclopedias, with events and characters spanning over a thousand years of history.

Heart of Darkness - Joseph Conrad as in weird unique, not a book I'd read again though

https://en.wikipedia.org/wiki/Heart_of_Darkness?wprov=sfla1

of course I knew of Conrad but i decided to read it because I loved Tom Neil's book An Island to Oneself (I've read that three times), non fiction. He was enamoured of Conrad.

https://archive.org/details/islandtooneself0000tomn

Infinite Jest by David Foster Wallace is mindblowingly impressive and cool, and I think well predicts a lot in it current culture and society, including technologically. Best part beyond the story is he’s just one of the most talented writers who ever lived.

My standard response is still Ridley Walker, though there are many other contenders ;)

Probably William Blake's Songs of Innocence and Experience. Blake hand painted the illustrations for each copy individually, so each copy is truly unique.

The Face of the Deep by Jacob Twersky. It's a novel written by a blind man about blind characters published in 1954. Its just a really interesting view into society at that time, the writer's views, and the character's struggles. Its not the best book but its certainly unique

[F-slur]s and their Friends Between Revolutions by the late Larry Mitchell is a fable written mostly in small poems about a society that marginalizes queer people as they build and rebuild their community. It was written in pre-HIV era New York, but is timeless in its chaotic radical fairy tone. It discusses some social and sexual practices rather explicitly, so if you don’t think it’s for you, it might not be.

I picked up a copy of a book called Raft by Stephen Baxter a few years back, knowing nothing about it. It was a bizarre story involving a group of humans getting stuck in a universe where gravity is significantly stronger than our own. I remember there was this strange flesh planet made of dead bodies. Interesting concepts but not sure I'd recommend it!

I'll say Wolf in White Van by John Darnielle. It's a non-linear story about a disfigured suicide attempt survivor undergoing litigation because he created an immersive fantasy game and two kids took it too seriously.

....Wow. Trying to boil it down to one sentence does not do it justice. But fundamentally it's a book about loneliness and how that can affect people in surprising and different ways. The loose, jumping timeline makes it feel like you're watching a car crash video after reading a news story about it: you already know exactly how it's going to end, but watching it happen kicks so viscerally.

And on the topic of John Darnielle, I also love Universal Harvester. It's the least horrific horror novel I've ever read. It's hard to point to anything particularly bad that happens in the story, but the mood is so intense and overbearing that you start to feel trapped, boxed in. There's a trick the author pulls about halfway through that was so subtle but so good: with just one word, the entire story got blown apart in a way that terrified me.

Quarantine by Greg Egan.

It's a really tough read. Simultaneous quantum multiverse tough.

https://en.wikipedia.org/wiki/Quarantine_(Egan_novel)

Clockwork orange

Close second: ancillary justice

Nothing to See Here by Kevin Wilson has probably the most imaginative plot of any book I’ve read in recent memory.

Reading Vladimir Sorokin's ‘Blue Lard’ felt like discovering Literature 2. It's not particularly experimental in regard to the structure, being a straightforward read starting with the beginning and ending with the end — although things are happening in a couple different timelines. However, throughout the novel my persistent thought was “what the fuck is going on”, while I was unable to put the book down.

Sorokin is basically Russian Joyce, doing what he wants with the language. In ‘Blue Lard’ and some other novels, he occasionally emulates the styles of classic Russian writers like Tolstoy and Nabokov, along with more general stuff like folklore and speech of stereotypical rural “simple folk”, and includes prose evoking the traditional manner of life. He mixes it with his own brand of sci-fi and a large helping of transgression, satirizes contemporary governmental attitudes and imagery, lampoons the worship of historical quasi-ideological myth, etc. He also has several stories that include nonsensical speech for some characters, while the overall happenings are clear as day to those who realize what they describe. This is true postmodernism, wherein if one has some knowledge of the culture, the threads to pull jump out from the page.

In USian terms, this is like if some author had nineteenth-century Americana set in modern time, complete with reverence for all the rural quirks and character, as well as entrepreneurial and pioneer spirit; emulating the tone and language of Mark Twain, Jack London and such, but mixed with some Chuck Palahniuk and ‘American Psycho’, and clearly taking a stab at contemporary politics in the most caustic way. And wrapped it all in a story as fragmented and outlandish as Vonnegut's ‘Breakfast of Champions’, for example.

A bunch of Sorokin's novels and stories, including ‘Blue Lard’, were translated to English — mainly by Max Lawton in an oddly short span of time. However, I'm not sure how any of it really translates, considering it requires some cultural context. I'd recommend starting with ‘Marina’s 30th Love’ (presumably not published yet), ‘The Sugar Kremlin’, maybe ‘The Blizzard’ or ‘Day of the Oprichnik’. Or, for aficionados of transgressive literature, ‘Their Four Hearts’.

Edward P Jones: The Known World, winner of the 2004 Pulitzer for fiction. It's about the complexity of slavery on a micro, local level, where a white man raises a black slave like a son, who then grows up to own a black slave himself, but that's far too simple a synopsis.

The best part was the structure, and the way he'd introduce characters. You're going down the road, and you spot a person. Then there is an entire section about the backstory of that person, leading up to the moment you meet them in the road, and then the story continues. After a while, every time a new character pops up, you get their fascinating back story, and you're right back into the plot. I actually caught myself saying here we go again, with a chuckle.

Virtuosic writing, deeply drawn characters, fascinating perspective.

Non fiction: Managing Neurodiverse Workplaces by Joe Biel and Elly Blue

My runner ups are:

• Native American DNA by Kim TallBear
• Junk Science and the American Criminal Justice System by M. Chris Fabricant
• Permission to Speak by Samara Bay

Fiction: The Gilda Stories by Jewelle Gomez

My runners up are:

• Ours by Phillip B. Williams
• Magic Has No Borders by (everyone on earth!?) Samira Ahmed, Sona Charaipotra, Sabaa Tahir, Sayantani DasGupta, Tanaz Bathena, Sangu Mandanna, Olivia Chadha, Nafiza Azad, Tracey Baptiste, Naz Kutub, Nikita Gill, Swati Teerdhala, Shreya Ila Anasuya, Tahir Abrar, and Preeti Chhibber
• The Cretaceous Past by Cixin Liu

The Slow Regard of Silent Things by Patrick Rothfuss: unique character writing and atmosphere

The Story of Edgar Sawtelle: unique plot and structure

Hitchhikers Guide to the Galaxy: uniquely whimsical writing style

Parable of the Sower: unique emotional force behind the writing imparted on the reader

Illuminae. It's an epistolary novel, so it's narrated in the standard sense. They are often told via letters from protaganists to another chatlogs, or other documents. From wikipedia about Illuminae:

The story is told through a series of documents; including classified reports, censored emails, camera transcriptions, and interviews

(I did not quote it in full because I'm trying to keep it as spoiler free as possible. I remember having a lot of fun when I read it without knowing anything, I just picked it up from the library and started reading.)

This book definitely wins for uniqueness of form, although I now understand what type of book it is and how to find more like that. But I've only ever read one book like that.

Although House of Leaves also counts a little bit as epistolary fiction but we've all heard of House of Leaves so that one doesn't count.

Though, 17776 - wikipedia, is even more unique and also epistolary speculative fiction, but that's not a book, but is instead online articles (which means it can include videos!).

You can start reading that one, right now, here: https://www.sbnation.com/a/17776-football

I would say "The Possibility of an Island" by Houellebecq. I don't recall much about the novel, but I remember that I was confused while reading it. It's a strange book.

Here's a summary: https://en.wikipedia.org/wiki/The_Possibility_of_an_Island

Surprised I haven't seen anyone mention house of leaves yet. Very unique book.

The weirdest story I ever read was something I randomly picked up at a bookstore called Touched by Venom.

I remember the main character underwent female genital mutilation and had repeat oral sex with dragons which are venomous and gave her psychic visions on how to get male dragons which were very rare and was how the economy was controlled. And her mother was a phoenix or something.

Maybe Gravity's Rainbow? It runs the gamut from repulsive to laugh-out-loud funny. It's also very long, bizarre, and frequently difficult to parse. Truthfully, I did not enjoy reading it a whole lot, but I did get all the way through and some of it very much stuck with me. It probably deserves a re-read, but I'm not sure I have it in me.

Probably "The Stones of Summer" by Dow Mossman.

It's often kinda gibberish but poetical anyways. Been a twenty years since I read it, but it stuck with me anyways. I can't say it's great, but it definitely exists.

Not sure if its the most unique but I picked up an old copy of a book called 'Apologizing to Dogs'. Very weird cast of characters and an interweaving plot. Strange book but fun to read.

Or 'A Journey to Arcturus' which is a weird-ass philosophical book dressed up as scifi.

Ceremony by Leslie Marmon Silko. A challenge (and a little silly?) to be sure, but vivid and mind bending.

Jitterbug Perfume by Tom Robbins. His work in general has a really unique feel, and i love his prose, but this one had the weirdest premise of all and he pulls it off beautifully.

My favorite book Gone Away World by Nick Harkaway features a fresh take on apocalypse/post apocalypse, with ninjas. His other works are worthwhile too.

The most novel book I have read has been Hagakure. I am not sure how unique it is; are there any other books written by a samurai at the end of the era of samurai? Dude had kind of a unique perspective on war and life as a warrior in a time where his class was no longer really needed. IIRC he wanted to perform ritual suicide when his lord died, but was forbidden from doing so as the culture rapidly changed and the practice was outlawed. He wrote the book because he didn't really have much else to do.

X X by Rian Hughes.

One of the books conceits is that certain character speak in a particular typeface.

Great science fiction book with a million twists.

The Magical Code of Regulations: A Fantasy Rulebook of Spellcasting Laws, Arcane Regulation, and Magical Compliance by Christopher Frigo

It's a legal code, written like a true legal code, except it's about magic use. It's really well done, not ment to be read cover to cover (like the real deal) but it's pretty trippy.

If you want to see an exemple of the content Ben Milton over at Questing Beast did a video about it.

The best AUDIOBOOK I've ever listened to was Sophie's Choice, by a long ways. The story is truly compelling, a worthy classic, but what made the audiobook experience so great was the reader.

Sophie's Choice features three main characters, with extremely different accents, one Polish, one Brooklyn, and one Southern. Throughout the book they have many lively conversations, discussions, arguments, and fights, and their accents flip back and forth from line to line.

The person who read it, navigated each change of accent perfectly, every time. It was a narrative tour-de-force. I could not have done it anywhere nearly as effectively iny own head while reading it. It was virtuosic reading like I've never heard before or since.

It is the only time I can think of where listening to the audiobook was a FAR better experience than reading it myself. It is easily the best example of audiobook reading I've ever encountered.

Dichronauts by Greg Egan. In reality my answer would be House of Leaves but that's already mentioned.

I still gotta say piers anthony's geoodyssey. plot travels through history with figures who experience the plot in total in different time periods but you as the reader see each part in each time period as a part. I mean I have trouble putting it into words for the way it works.

Tracy Kidder’s The Soul of a New Machine (1981) stands out as a landmark work because it transformed computer engineering—traditionally viewed as dense, dry, and mechanical—into a high-stakes psychological thriller. What Makes It Unique

• Literary Treatment of Engineering: Kidder was one of the first journalists to apply narrative non-fiction to microchip design and system architecture. He made circuit boards, diagnostics, and 32-bit minicomputer logic as dramatic as a heist novel.
• Unprecedented Access: Kidder spent over a year embedded in the basement of Data General in Westborough, Massachusetts, gaining raw, unfiltered access to Tom West’s clandestine engineering team as they built the "Eagle" (Eclipse MV/8000).
• Defining Tech Culture Early: Written before the modern startup ethos was mainstream, the book captured the nascent psychology of tech work. It popularized terms and concepts like "signing up" (voluntarily agreeing to extreme overwork and personal sacrifice) and the "pinball effect" ("You win one game, you get to play another"—the reward for finishing a hard project is just the next hard project).
• Focus on the Humans, Not Just the Tech: Rather than focusing on corporate strategy or hardware specs, the narrative centers on the obsession, burnout, ego, and quiet brilliance of young engineers driven by the craft rather than money.
• Literary Recognition for Science Writing: It won both the Pulitzer Prize for General Nonfiction and the National Book Award in 1982—an extraordinarily rare feat for a book focused on computer architecture.

I’ll also mention Dhalgren by Samuel Delaney. I felt like I was on drugs while reading that book, loved it.

Any of the weird fiction by Steve Erickson, but this is probably my favorite: Tours of the Black Clock