Went and saw this with my sister yesterday and it lived up to the hype in my opinion. Good and creepy. At it's best, it reminded me of movie's that have scared me in the past (Rosemary's Baby, Exorsist, The Thing, etc.) True, there weren't a ton of scares, but it mounts as the movie goes on. Three times my sister and I, both lovers of good horror films, found ourselves reaching across the seat between us and holding hands. Not something I do lightly.
Slight spoilers ahead.
Towards the end, theres a scene where Katie is lying in bed and, after all that has happened in the house, she changes her mind and wants to stay there, feeling it's safer (you could pratically hear everyone in the audience shaking their heads "No!") As the scene fades, and you realize they're spending another night in the house, someone in the back of the theatre goes, "Oooooh shit."
We all laughed. It was a tiny, weak laugh, but a laugh none the less. We knew we were all in the next twenty or so minutes together.