Basically, the picture above shows where'd I'd go with a TMNT film. I'd have it in the Sin City/The Spirit style. The film would be less kid friendly and more fan freindly, staying more true to the comics (maybe introduce April in a sequel?). I can't say that this would work, but I think it'd be pretty damn cool.
Here are some pics for visual reference, in case what I'm proposing has been confused: