People are saying things about 3D World being "based around multiplayer", but the thing is it's not. It's really just a single player game, but with multiplayer added on. Mario Kart is a game that is based around multiplayer and that's why it has online and local.
Multiplayer is really just a bonus in this game, and it's not nintendo's fault if you have no friends who are willing to come over and make use of it. Local multiplayer is much more fun anyway.
Local is much better but online should be included for those that can't afford several controllers/ don't have friends that want to play. The gamepad even have a mic you could communicate with or even a virtual keyboard on the pad, I would love to play with some of my friend's that live 2.5 hours away 3-4 times a week instead of twice a year.