Great little splatterfest. It'll probably be one of the better movies this year.
A couple nitpicks. Don't movie makers realize that the actor chasing the runaway pet is tired and annoying? Everyone who chases their pet gets fucked up. That's why I never chase after my dog.
The bad guys weren't scary enough. It was like the Toxic Avenger was trying to play Leatherface.
The mutant expaining the reason they were eating everyone. As if enough clues weren't crammed down your throat through, I don't know, the entire movie?! They could have left the explanation out and (most people) would still get it. It would be scarier too.
All of these nitpicks are forgivable. Alexandre Aja is going to be a master horror director.