Intelligent film masquerading as trash
I'm surprised by how many people on here failed to understand this film.
This is not a movie for your typical slasher fan - this is a movie for true cinema nerds who've seen lots and lots of films in many styles. It plays with genre in a way that few other films do - the closest thing I'd compare it to is Donnie Darko, but it's much more irreverent and "meta" than that film, or maybe "Cabin in the Woods" but it's much funnier and creative than that film.
What may be confusing people is that it acts as if it's a teen movie, when it's actually a commentary on teen movies. It looks sloppy and ADD, and that's intentional. Joseph Kahn the director has made some awesome films, and he's an opinionated student of film. Listen to him discuss this film on one of the podcasts he's taken part in, and you're likely to re-evaluate this movie.