It all depends on what kind of gamer you are. The graphics are substandard for today's nextgen consoles. However, you also need to consider the "fun" factor. Wii is really geared towards social gaming. If you play together with friends or family it can be extremely entertaining and easily take up a full evening, even just playing the simple Wii Sports that's packaged with the console. That's not to say there aren't standout solo games on the Wii: Zelda, Metroid Prime 3, and the Mario titles come to mind quickly. There are just fewer of these games on the platform than on the other big boys, and there is a lot of crap out there as well.
Considering the price, if you are going to play with others on a regular basis, I think it's well worth it, especially considering you should be able to sell it pretty readily on the used market if you decide not to keep it - as far as I know, the demand is still outpacing the supply, so the used market should be pretty healthy for the platform still.
As an aside, gorgak is right, you can reduce the motions of the controller to quick twists of the wrist, but that defeats the purpose for me. Most of the games on the Wii that are relatively popular are less about plowing through the game and "winning", and more about having fun. Yes, I could use wrist movements to play Tiger Woods, but why? It's more fun to me to worry less about the score and get immersed in the gameplay and fun factor of emulating a real golf swing to play the game.