See this on youtube while you can, because it was playing theatrically just a year ago. (film is not embeddable; click image to link to video page)
It has some faults. I don't find either of the two lead actors to be appropriately cast, and I strongly dislike the score. And in terms of pacing, it may be even more glacial than director Ti West's previous critical smash, House of the Devil. That isn't necessarily a bad thing, although it's a style that's not to everyone's liking. I think it's genuinely scary, and a true anomaly in the current trend of movies; the slow-burn horror film.