The main problem with Sucker Punch is that it has severe pacing issues--while the "dream" sequences are huge on the action and keep you at the edge of your seat, the rest of the movie is too slow by comparison. This isn't terribly unusual, but the highs in Sucker Punch are so high and the lows are so low that it just doesn't work very well. It also would've been better if they'd just gone for the R rating instead of trying to stay PG-13.
The theatrical version is best watched as a feature-length music video, not a movie. If you think of it like that, it's a lot easier to enjoy it.
The extended edition on blu-ray, IMO, really fixes a lot of the pacing issues and levels it out some more. That should've been the one that went to theaters, but they were trying too hard to avoid that R rating.