I enjoy "different" horror movies. I'm not interested in torture porn and gore and people getting chopped up. I want something INTERESTING, whether it's Lovecraft or weird time travel or alternate dimension or thought-created nightmare stalkers - there has got to be a "WHOAH!" for me to enjoy horror movies.
This movie was one of those, with the caveat that, though I won't spoil the ending, if you loathe movies that leave some lingering but relevant questions, you may not cotton to this film.
But like me, if you can separate this "style" of movie-making, which I've seen some just call "lazy", the actual progress of the people and actions in the film were compelling and it is definitely a mystery type horror movie, though not a room-to-room-magnifying-glass type.
If you saw and liked Coherence and I see people are comparing this to Phantoms (I haven't seen that yet, somehow), or if you like the "unknown/invisible", creeping ominous threat movies like Mr. Jones or Resolution, I think you may enjoy this film.
I'm not saying it's perfect - there's a good amount of irritation at a few of the way things go down or people behave, that I felt kept it from being more fluid, and while the acting is by and large at least decent and believable, there are some boneheaded decisions - but not like most horror movies, at least not as frequent - it really doesn't get a chance to build to that level before the horror is in play.
I did like the dialogue for one of the characters, who was a modern sci-fi and horror movie type that was constantly referring to what was going on as something from Stephen King or aliens or zombies or "the spirit of an ancient Indian burial ground", which made me laugh - he seemed the most "real", well, until later, but that's not germane to the point.
Anyway, a lot of people on forums and other sites are giving this a really low rating, and while, for the overall and idea of a complete story, I can kinda see why... I still think what there IS there is good and different and not anything close to "usual horror movie stuff".
I would have given it an 8/10, but I had to stop at 7 because of the unsatisfying or at least not well-enough intimated ending, because I agree with some people that say the "figure out what YOU think it means" is one thing, an artist can't show you a pristine, untouched canvas and say "just IMAGINE the awesome picture YOU want there!".