I beat the game in 15 minutes on Easy. I'm going through on Normal with Donatello right now (taking a break). Co-op on easy is too easy, even with a lot of chaos going on. Level 3 is a mess IMO. Also, they put in double jumping for some stupid reason. What do I like about the game? The 3d combat. It works pretty well, although it'd probably work better with a Dualshock.
What do I not like about the game? The scrolling. This is pretty bad. The final boss fight took me 5 minutes because he kept going off-screen and the game didn't scroll until I basically got to the edge of the screen (Where he was to greet me with one of his lovely attacks). Also, online the game kinda, sort pseudo-scrolls with the host. Once again, level 3, too much crap going on, if the host is at the front, and you're at the back, spike fence is nailing ya. Also in co-op, you cannot quit during a level, only after a level.
Survival Mode on Co-op is something I wanna do for the Achievement. It seems like the only way. Why it's Normal or higher is beyond me because they shouldn't have put Easy mode on there for it.