It's super slow to start, trying to create a storyline and give you background of the girlfriend's (Katie) past rather than just throwing you the scary stuff w/o you knowing where it came from ... which is good, but it drags on and on.
But once it starts to pick up it doesn't stop and you're constantly thrown something more intense. I got so scared I teared up.
It is also funny ... in a morbid kind of way, because of the comments and things that the boyfriend (Micah) does.
You MUST see this movie if you have been waiting for one that will actually scare you. It's easier to make scary movies that are gruesome, it's harder to make one's that make you terrified. Terrified was reached.