Return of the Living Dead Part II(1988)

Go old-school. Classic, underground, teen, zombie flick.

Hereditary

How about The Green Room? It didn't even register as a horror movie until it was too late.

A few off the beaten track movies that come to mind:

• Haute Tension
• The Descent
• Rec
• A Girl Walks Home Alone at Night

It's going to sound crazy but after reading your comment about not wanting gore, the perfect movie might be the Texas Chainsaw Massacre (original.) It's just super creepy throughout but with impressively little gore etc.

Last Night in Soho is a mishmash of films but gorgeously shot with a sense of style, in some ways a love/hate letter to London in the 60s.

And finally, a weird one that I really dug, It Ends. It's not at all like anything else. I saw it called a hang out horror which is as good a description as any.

The original slasher Black Christmas (1974) holds up well; unsettling, bleak, and scary imo

Rec, it's a pov Spanish language horror from 2008 but set in a building that could easily be a setting for 70s-90s. Kinda like Blair witch in a haunted house. Some jumps but the suspense is built for the bigger scares.

Candyman (1992) it's not exactly unknown but I think it's recognition falls behind other 90s horror movie& series. Philip glass soundtrack, multiple conflicting myths & legends, scares that are suspenseful and gory and unexpected.

There are a couple alternate soundtracks to Nosferatu (1922) that make it more scary and less dated

Edit: for more thriller less bloody I'd go with Hitchcock & the movies he helped inspire like Brick, Blue Velvet, Dark Passage, Basic Instinct

The Others (2001), The Orphanage (2007), 1408 (2007), The Skeleton Key (2005), A Dark Song (2016).

Alien (1979)

Oddity

The Substance

Harry and the Hendersons

I love horror movies, but haven't found much time for them in recent years. The two I have watched relatively recently were Hereditary and The Ritual. Both were pretty good for different reasons.

Event Horizon may be on the fringe of what you're interested in based on the comments.

The Serpent and the Rainbow (1988): takes place mainly in Haiti, where an american anthropologist is attempting to study rumors of zombie resurrection only to find himself caught between the combination of the Tonton Macoute and Voodoo occultism

Salem's Lot (1979): The original miniseries (2 parts iirc) This one has one of my all time favorite Nosferatu style vampires, along with Richard Straker, a very proper and suspicious antiques dealer played by James Mason

Texas Chainsaw Massacre 2 (1986): Silly as it may seem to recommend a sequel like this, Texas Chainsaw Massacre 2 is pretty wild and introduces Chop-Top played by Bill Moseley who is simultaneously disturbing and hilarious, always in a horror-y way.

These are probably like a 5-7 out of 10 for scariness, but are some of my personal favorite horror movies, one more recommendation which I'd give a somewhat higher scare value, but isn't in that era is

Frankenstein's Army (2013): Neat storyline, and some really cool practical effects. (Not army of frankensteins which is another film entirely from 2014)

top would be sinister. im not easily disturbed by horror movie but this one did a good job. Its from 2012 and takes present day but also crosses time. its a bit hard to explain and its best not to.

The innocents with Deborah Kerr.

The Empty Man

Out of the latest Abigail and Bugonia are fantastic. An old classic - Gerald's Game. Black Phone was surprisingly good.

Edit: only now noticed you want them to be set pre-2000s, oops, sorry. Oh well ;D

It Follows

The Presence (arguably not a horror flick)

Saint Maud, a fanatically zealous Christian girl moves in with an aging ballet dancer to care for her. Religious mania and weird supernatural shit ensue.

The Ritual, 3 friends on a hiking trip become lost in an increasingly creepy and haunted Scandinavian forest.

Suspiria (remake), a German dance academy hides a bloodthirsty coven of witches. Not nearly as visually striking as Argento's 1970s original, but MUCH more coherent as a story.

No One Will Save You

Abigail

A Quiet Place

My favorite horrormovie of all time is REC 2.

Carnival of Souls. If you don’t mind black and white movies, this is easily one of the creepiest surreal horror movies ever made