For one thing, it is pretty violent for a PG movie. Lots of kicking, hitting, punching and things you'd want from a Ninja Turtle movie. It really wasn't too campy. Sure, some of the jokes weren't funny but they weren't on the bad joke level of the previous movies ("Help! I'm a turtle and I can't get up!" anyone?).
If nothing else go see it for the fight between Leonardo and Raphael. The coolest scene I've ever seen in a CGI movie.
Really it is a great movie, and while not as dark as the original comics, I think it's great for what it is.