My rec would be the original Halloween. It's the only John Carpenter film I've seen, but it's really good. I'm not a fan of slashers these days, I used to like them when I was younger but lately I've found them boring. For instance I saw the film X recently, about some people in the '70s who rent a small cabin on a farm to shoot interracial porn but outside of the big studio system, and then they all get killed. And it's a well made, well written movie. It's got lots of little twists on the classic slasher formula. But once you get right down to it, it was a slasher, nothing that special. I don't regret having watched it, but it's not going to leave a lasting impact on me. But Halloween, the first big slasher film, is just good all around. Even now, even having seen all the derivatives it spawned, the original holds up.

Ditto the original Texas Chainsaw Massacre.

But all I really wanted to say is that The Ritual is such a good movie. I happened to stumble across it on Netflix not knowing what it was, expecting something that would play in the background while I browsed Reddit. But it blew me away.

The Witch is probably my favorite horror film.