So you like horror movies but you're also a discerning adult that enjoys sophistication and subtlety and so you have to endure lengthy periods of time without anything to placate your creepy cravings? Then there's two of us! And I should stop yammering right now and just direct you to
Kill List, which is so good a movie I'm pairing it with
Rosemary's Baby in the groin-grabbingly good department (just so you know where I come from, I consider "Rosemary's Baby" the best horror movie ever made). It's funny how there are so many inverted parallels between the two movies (just an example, in "Kill List" it's the husband that's put through the grinder).
If you go see the user reviews at imdb, you'll notice that it's 10% people writing extensive, well-written and thoughtful analyses on the movie's merits and overall awesomeness, and 90% angry people fighting with their keyboards. That's the tell-tale sign of a movie that doesn't give you all the answers in the end, even though it's all there for you to pick up, even if only in a suggestive manner - more than enough to keep you mulling over it long after it's finished (and if you've seen "The Wicker Man" and "Rosemary's Baby", you'll see what's afoot pretty early on).
Things that I absolutely loved about it: The improvisational feel of the dialogue; all the main cast; the delirious and yet understated use of symbolism (there's an absolutely unnecessary, mad and gorgeous shot of the two main actors stepping out of a car under a rainbow that is just the stuff of genius, considering what's happening); the soundtrack; the photography; the humor, so dark it's blue; and even though I'm not one to praise the depiction of graphic violence when that's all a movie has going for it, the violence in "Kill List" is well-earned. Go go see see it it now now.