It's Short, so It Sucks: The game has very little content. A story mode that lasts a whole 30 minutes, a repetitive survival mode, and 51 extremely short honestly-not-stolen-from-Super-Smash-Brothers-Missions. That's it.
The Scrappy: The threeRaving Rabbids are hated for being very out of place and nonsensical even in the context of the publisher, their brand of humor not fitting the game, and wasting slots that could have gone to well-known TMNT characters.
So Okay, It's Average: Some people defend it as a decent fighter (especially good for a licensed game) while others attack the small roster and lack of major TMNT fanservice, but the general consensus is that it's this. Disappointing, considering it was made by one of the same devs who made the critically praised Brawl.