I saw this today, with my sister and a family friend. I'm pretty unsure how I feel about it, it's a tough one to rate. I'll try not to be specific here to not spoil it.
First of all, it was gross. I'm usually pretty solid, but there was more than one scene that made me look away and cringe. Although that's not sufficient to be a good movie, it's a nice change from the ordinary. They didn't shy away from totally disgusting the audience. It's rather like Saw 1 in that respect, except darker.
Next, I like the characters. There was pretty good character development for most of the main characters. The protaganist character is a cop who starts by looking noble (searching for his son), but during the movie is shown in a darker light. The antagonist starts out seeming like a maniac, but as the movie develops and you see more of his motives, you (or perhaps I) actually feel some empathy towards him. He's torturing people, which you'd know if you saw the first one, but he's also trying to get them to help themselves. I guess that's as good a reason for any to torture, but I rather like what he did.
The action was great. I like how the story unfolded. I enjoyed how the antagonist was present and talking for almost the entire movie, that was a great effect in my mind.
Now, the problems I had. This paragraph is as close as I'm going to get to a spoiler; read at your own risk: I found the movie was very, very dark in terms of mood. In most movies, it begins on some action, then has some calmness/happiness, then gets dark. This movie had no such thing, it started bad and went to worse. I felt no comfort at any part, and it was almost stressful watching it.
The other problem I had with it was that they did a lot of really quick transitions. Like, they show lots of scenes really fast with loud noise to create an effect (I hope you know what I mean), but they do that WAY too much. It's way overused.
Overall, I think that if you want a movie that's going to totally gross you out, it's a good one to see, but it's not for the squeemish/faint of heart. Oh, and I wouldn't recommend this movie for Quik. If you see it, hopefully you know what I mean