A big ass 17 baby!
I haven't tried all that hard to get a huge number though, but I will, bwahahahahahahahaha.
As for this game being in 3D, that's true. It feels like the oldschool games because, when you really think about them, they all FELT as if they were sorta in 3D, seeing how you could move back into the background and everything like that. It really feels like they just took one of those old games, updated it and fleshed it out, and gave me exactly what I wanted.
I wasn't trying for mine either, just starting slashing at a group of about 6 people, and bam, got 20.
Thinking about it tho, your assessment is pretty true about the game. It does seem like one of the old 2-D games, just with a new camera angle on it. But of course anything with the Turtles in it is gold anyways