Sometimes hype hurts a movie just as much as it helps it. This was definitely the case in Paranormal Activity; it's only the hype that gets this movie distributed and gets people interested in going to see it, so that's good for the makers. The problem is all that hype gives people expectations that the movie just doesn't live up to, which sucks for the audience.
There was about as much explanation of the "haunting" in this movie as there was in the Blair Witch Project, which was kind of a bummer. It had some creepy images, but otherwise it was just too flat.