Two pleasant horror surprises in one week. Groovy.
Where Dead Silence proved to be a homage to old horror, this one is a little ...more modern - nastier, though only for the fact that the tone throughout is about two notches into the more serious. It gets intense quickly, especially with the decision to show us so little of the antagonists - that worked.
This is a pretty decent horror movie - I'll be curious to see a sequel, that's for sure - it had a few really good jumps, and a setting that worked extremely well.
I'd guess complaints will stem from that somewhat ambiguous ending, but holy shit do I ever like those. It is a peculiar particular choice to do that with any film, but I have a damn good imagination - I like it when it has to do some work.
Certainly not hard to tell it came from the Paranormal Activity gang, but again - that's alright, keep 'em coming.
This isn't a great movie, but I'd happily watch it again ...preferably with really jumpy friends.