This movie has a lot going for it, but ultimately doesn't do anything new. I liked the raw, gritty feel of the camera work. This movie used the first-person POV really well. It isn't a gimmick that you will say, "Why would they be filming this?" It is internally consistent. I liked the characterizations of both the villains and the victims. They all seem to make choices consistent with their characters. I also like the setting a lot. It seems plausible and fits the terror of the movie.
The issue is that, when you finally reach the end, there isn't much to remember this one by. The story has been done a number of times. The practical effects are good, but not special. The villains are threatening, but not memorable.
I liked this one and I recommend it, but its not a classic.