Going by what Letterboxd lists as horror.
1. Antichrist
I never used to think of
Antichrist as being horror... but I guess it is. Wiki describes it as "experimental horror," which I think is an apt description. Alas, it's one of my top favorite films of all-time. I find it to be intense, visceral, and f*cking stunningly, beautifully crafted. One of the most atmospheric films ever made, this is a masterpiece to behold.
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2. The Witch
Another masterpiece. I read someone describe it as Ingmar Bergman meets Ken Russell (I'm guessing specifically
The Devils), and I think that's proper. Elegant, well-crafted and at times a bit disturbing, I couldn't stop thinking about the film for quite some time.
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3. Let the Right One In
It might be my favorite vampire film, like it is many. It gets a lot of recognition among people and I think it's well-deserved. Another atmospheric, well-told story of puppy love... one of those pups being a vampire!
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4. Lords of Salem
Including this might make me look bad, and it's based more on my memory than anything - I've seen it once, and seeing it again, my opinion of it could drastically change. The only reason I provide that caveat is because I'm kind of confused why I like it so much. I haven't heard many say anything good about it, and instead quite a bit of bad. But I find it to be another elegantly-made, subtly-paced horror film. I love the brooding nature of it... the slow zooms when he establishes shots, for example. It's the only film by director Rob Zombie that I like, by the way. It is so different from his other work, and I wish he'd do more like it.
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5. Stoker
Like
Antichrist, I'm kind of iffy about this film being called horror, but Letterboxd and Wiki both say it is so whatever. I love this film for a few reasons. The main one is Mia Wasikowska. She is such a joy to watch in this flick. The second main reason is Park Chan-Wook's directing. Stylistic and atmospheric. A great, underrated film.
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6. Pontypool
I first saw this early last year, and I freaking adored it. I gave it a full score and immediately rewatched it. Recently, I saw it again with a friend and loved it just as much. It's a great, creative film, that doesn't rely on blood, guts or nudity (not that there is anything wrong with those things, but the change of pace can be refreshing), and replaces them with bold originality in script. Love it.
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7. The House of the Devil
The pacing! The glorious pacing!
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8. May
I dunno. I guess this film relies a little bit on the charm of Angela Bettis, but I feel like it works so well anyway that I decided to include it. Lucky McKee is an awesome modern horror director, and this is his best film in my opinion (though
The Woman gives it a run for its money)
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9. Ginger Snaps
It's a classic, and one of the best werewolf films.
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10. The Babadook
The best performance of anyone on this list (though not necessarily my favorite to watch) has to be Essie Davis as the mother in this film. She's brilliant. You can feel her anxiety and mental breakdown - says someone who has dealt with both those things himself. The kid is good too, properly annoying.
I feel like this film got some backlash after it came out and some said how scary it was. It's not scary! But that's okay. Horror films aren't scary, and that's not why I watch or like them.