The more "styles" they'll add, the more likely I'll buy this game. The New Mario inclusion is already very welcomed! But everything will depend on the sharing: I'm not a fan of creating levels, but if I can download potentially infinite New Mario (and old Mario!) levels to be played with the usual good playability of Super Mario platforms, I'll be totally in.
Mario VS DK and Pushmo are a good hint at what they'll probably do for level sharing I presume