The movie at first seems like it's going to do a good job of slowly escalating realistic scares (omg did you see how the door just slightly moved??), when all the sudden there's this huge animalistic shriek, and a BANG against their bedroom wall that rocks the whole house, and would 100% have gotten their neighbors to call the police. It's not scary, it's like watching found footage of a bear charging someone in the woods. Yeah, that's a situation that would suck to be in, but I'm not in the frame of mind to be scared of demons. I'm now acutely aware that this is a movie.
It never improves from that point, the scares continue to "escalate" less and less convincingly until finally climaxing in the possessed Katie throwing her dead boyfriend across the room into the camera. She then creeps up to the camera with very cinematic intent, and finally lunges for one last scare.