PERSONALLY... Judging by the size of the mat which came with Mario Mix, I would say that it was for younger kids. (Minus that damn Bowser stage on super hard mode. >>;

So I'm actually not one to judge.
Now, aside from the, er, difficulty-level aspect of it...
BOWSER BREAKDANCING SCARED THE LIVING CRAP OUT OF ME. So did WARIO DANCING. As in WARIO DANCING PERIOD. DX "WHY?" I cried. "WHY???"