It's worth buying if you have friends that are willing to play the game.
The Good: Well, for one, you only need one Wii remote, which are becoming harder to find recently. But, above all, it's a simple, enjoyable game. Anyone can play. This game has a lot of replay value, you'll find yourself playing single player over just to unlock new minigames.
The Bad: Singleplayer is the main flaw; it's far too short. You can beat it in about one hour if you're familiar with Wii controls. A more minor flaw is the lack of game descriptions; it'll usually give you a one-word instruction, and the rest is guess work.