Ryu doesn't have an RPG. Samus doesn't race karts. And Link has never played Sonic in the Winter Olympics. What am I saying? I'm saying that whatever you're looking for, Mario has it.
Okay, he doesn't have a gritty shooter yet but zombie survival is coming to Mushroom Kingdom no earlier than 2014. For the most part, what you want, Mario has. And whether you prefer your games in 2D or 3D, Mario's got both. Hell, thanks to Paper Mario, Mario can come as close to 1D as any game since Pong.
So next time you're praising a franchise, ask yourself: would this protagonist take the time to teach me typing? If it's not Mario, the answer's a no.
The Mario series isn't just about variety; it's how deep it goes. There isn't just one good Mario RPG and there isn't just one cool Mario sports game. No, the series has done the near impossible. It has made great franchises within a great franchise: Franchise-ception.
There are no fewer than three good games in every franchise within the Mario universe. For RPGs, there's Super Mario RPG and three Paper Marios. There are more Mario Parties than any man could play, enough Mario Karts to give you blue-shell-trauma, and even three Smash Bros. games to cover your fighting game fix.
And before you call Smash Bros. anything but a Mario production, ask yourself: what other Bros, outside the Mario bros, are doing the smashing? Exactly.