It's essentially a brilliant sci-fi movie... for the first half hour. I felt like there was so much mystery and intrigue, a perfectly built world, everything was just clicking for the first half hour.
Then as it went on it got a little worse. It's not enough to come close to sinking the movie but the quality does decline a bit. I still think it's a fucking great movie though. Not amazing, but great, definitely worth a watch. It's pretty gruesome and well made all around, the script could just use some work.
What makes it great, in a nutshell, is that it actually feels like a legit sci-fi movie. It was OBVIOUSLY in the hands of somebody who knows sci-fi, somebody who knows that a sci-fi world should be interesting and different, have a life of its own. None of this bullshit where other "sci-fi" movies "create a world" that is boring as piss. There's nothing worse in sci-fi, or fantasy, when a movie just doesn't feel like it's taking place in some different world. It can take place on Earth, but it needs to feel like science fiction. Not just HEY WE THREW IN SOME FUTURISTIC SHIT FOR YOU. I know I'm probably not doing a good job of explaining what I mean.