I think they need to expand their character set. Don't get me wrong, there's a lot of choice, but who really wants to play as Baby Mario? Give me Link, Samus, Kirby and Pikachu already.
Me and the GF played some online the other day; she's not a gamer at all (aside from the occasional iOS game) and so struggled a little. She couldn't get her head around drifting/bouncing over jumps, and this cost her a little time on corners. That aside she did okay. I'm a little disapointed that we didn't keep the Wii's co-op online play. I really enjoyed driving around whilst she threw shells at people.