I went into this without having read the book this is based on. Even if this had not been based on a novel, I would have been impressed. The plot keeps you guessing right to the very end of the film. I found myself immersed in the environment of the characters. I felt some of their fear as new unpredictable things began happening one after the other. All actors involved played their parts superbly.
The rating is spot on for mostly bloodless and implied violence, frightening monsters and some somewhat strong language. Definitely worth your time if you're into future dystopian mystery thrillers.