Although the whole "mature Mario" idea sounds dodgy, I am very eager to see how this game turns out. Because, you see, I think Myamoto knows what he's doing.
He is not one to be easily swayed by what the "Industry" thinks is cool or mature. He was right there, a key creator of the Industry! He know what makes a good game, and he (should) know(s) what his fans want. He will not let these little Sony weeners tell him what's in.
I expect the Mario Bothers' basic image to stay the same. Hats, overalls, colors, you know. I expect much better graphics, slightly more on the realistic side than the cartoonish. I expect a more challenging game. One in which the bad guys can actually kill you and you have to be fast on your feet.
I do not expect anything that would raise the current "E" rating. No cursing, no blood or guts, no sexual references whatsoever.
Basicly, I expect the same old, just better.