WarioWare: Smooth Moves is very fun. 9.5 out of 10. The story mode is kinda short, but the multiplayer is very good. I like playing Wario Dance Company Microgame on super fast speed. Also Super fast speed on the driving one is fun too. Smooth Moves is a great multiplayer game and you can play up to 12 people multiplayer!
I would suggest waiting for Super Paper Mario or Super Mario Galaxy if you want some 1-player action, but Smooth Moves is a great and easy to pick up game.