I was disappointed overall with the movie, especially with all of the hype surrounding it. I love a great horror movie, and the idea sounded like a lot could be done with it. It definitely had its creepy moments, but those without any imagination will have a problem becuase there isn't any gore or in your face special effects to jar you. I think the pacing might also be an issue for some. A few couples walked out, not because it was too scary for them, but they got bored waiting for the payoff.
The finale is reminiscent of the Blair Witch Project, in that it gives you a creepy ending that will have you thinking about it after its over, but not quite terrifying enough to live up to your expectation.