I just got back from seeing this. I thought it was good.
I'm not a big horror fan, but this film is definately one that will transend the genre sort of like The Ring and The Sixth Sense did. And guess what? This movie is actually scary; imagine that, a horror movie that's actually scary.
The plot is easy to follow and it doesn't leave you scratching your head thinking what the hell was that all about. Everything makes sense, except for all the dumb things some of the characters do, but I suppose that's pretty standard for horror films.
This is definately one you want to see in the theater. Preferably one with a packed crowd. I see some people saying they will wait for the DVD. Big mistake. You'll regret it later.