When you create a... conceptual void, no pun intended, around the main mystery of the movie, leaving it to the viewer's imagination - that's one thing. But when you straight out just don't tell us anything, and leave an entire movie up to the viewer's interpretation, why not just let us stare at the blank screen, and imagine our own movie entirely, the one that's better hopefully. The visuals are very interesting and creepy, there's a great practical effects work done here, but they alone can't hold the movie! We don't know anything about the characters at the beginning, and we know next to nothing at the end. The characters themselves have no personality and are reduced to a single characteristic by which they can be recognized - the cop, the nurse, the old guy, the pregnant lady, the angry guy, the young guy, the bad guy. They're all boring and unlikable. I guess this movie is OK if you're stoned and just want some heady visuals, but that's about it.