I don't consider anything I watch a guilty pleasure, since I'm pretty open about watching B and bad movies.

I enjoy movies where a director has made a surprisingly successful cult movie and on the back of that got creative freedom and a big budget from a studio, which they then used to create something beautiful and terrifying. My exemplar movie for this is Southland Tales, which I absolutely love on all possible levels.

I really like movies that commit to a sharp genre turn. The Guest (2014) is a great example.

Lastly, spaghetti westerns. This seems like a maybe more mainstream choice, but had a conversation in real life not too long ago with somebody who had no interest in any kind of western and didn't know about the distinction between classic and spaghetti. When I was articulating the difference I was able to boil it down to classic westerns being nostalgia and romanticization of the American west, while spaghetti westerns were made by people with no nostalgia for it. It creates a subgenre which is grittier and more morally grey than the John Wayne era movies. My favorite is Once Upon A Time In The West, though I'd recommend people work up to that by watching other genre movies first.