The wiki entry for Hansel and Gretel best describes the movie and what I think is the general consensus about it - "unpretentiously entertaining." This is a movie that doesn't care about being anything other than a fun romp that doesn't take itself even the least bit seriously. When done the right way, a movie with this attitude can be a huge success, especially when it is backed up by some fun action gags and decent enough story that at least keeps things moving. Some stuff was obviously filmed specifically for the 3D aspect (hate that), but it's not too much and doesn't distract.
The CGI effects are obvious, but not unbearably so. The CGI blood makes the kills feel a bit tamer and PG-13, though, so some cool kills are left feeling a little less cool and not as hardcore. At the same time, this is exactly what I was expecting and I wasn't that disappointed with what I got. There's a guy exploding in a bar, the Sabbath massacre, and probably my favorite part - the troll head-smashing sequence. So sad about Stormare, but he went out in an awesome way.
A very surprising thumbs up for a movie I wasn't expecting to like at all! Hansel and Gretel: Witch Hunters is simply a good time all around, a movie with a good sense of humor and unpretentious understanding of what it is. Bring on Part 2!