What was wrong with the movie? Everytime I ask this (not just here, but in other places) nobody can describe why.
The first movie had great action, the second toned it down a bit but was still pretty good for comedic fighting but the third really took the cake with slapstick and while that in of itself didn't make the movie bad it certainly didn't make it better.
The suits were nowhere near as great as the Henson ones but I can forgive them for that since they still worked fine.
The storyline was just kinda... meh. I actually liked how they incorporated Japanese culture but the characters weren't very memorable nor likable.
The comedy wasn't really up to par with the previous two movies either though it had it's moments and some of the best known one-liners from the TMNT movies "help I'm a turtle and I can't get up" and "I think I swallowed a frog" for instance. And the culture shock for the samurai hanging out with Casey was at least somewhat amusing.
The sub-plot that some of the turtles didn't want to go back home was one of the more interesting parts of the movie. Not shockingly this was yet again something else Leonardo and Raphael didn't see eye to eye on.
The relationship between Raphael and the little boy Yoshi did a fair job of showing Raph's softer side.
The final battle made Shredder's pathetic losses in the first two movies look impressive by comparison.
All and all it's not a BAD movie in my opinion but it's easily the worst of the 4 (I'd rank it TMNT I > TMNT 2007 > TMNT II > TMNT III personally).
It's one of the most light hearted incarnations of TMNT to be sure and that's already off-putting to some fans but it's not even really good at being light hearted entertainment but it at least it isn't boring like some of it's immitators *coughWarriorsofVirtuecough*