I saw this a few weeks ago. It was fantastic. I'm a huge horror fan (I even sometimes go to the Fangoria conventions and whatnot) and think this movie was easily one of the best "horror" movies in recent years. Definitely one of the creepiest and most genuinely scary movies in a long time.
Tip: never see a horror movie on a Friday or Saturday night. That's when you have to deal with stupid people in the theater. Also, when people laugh in a scary movie, it's not because they think something is actually funny. Instead, they laugh because the act of laughing is a natural response which helps the body ease a sense of fear and to calm the person down.