Anyone ever delved into virtual reality environments? It's a LOT like the Wii. The way your movements control the actions, etc. And guess what... it SUCKS BALLS! The Wii is revolutionary in that it brought this interactive capability to the everyday console. However, this would be betting that the novelty will be enough to carry it its entire shelf life. I would be willing to bet that this idea will fail in the long run.
I don't doubt the Wii will sell like hot cakes. I bet it'll out-sell every system out there. However, I also believe, because of the fact that the novelty of the system will wear off quite quickly, and the onset of how shitty VR-type controls are kicks in, the sales of games will drop dramatically. This will leave the Wii where the Gamecube left off: in a pool of semi-mediocrity.
Oh, and many of you are probably thinking, "Noooo. These controls kick ass. The gameplay is amazing! OMGZORZ!!!" Kind of like how f**king a girl and living with her are two very different things, how many gamers actually WANT to be active? Why do most people play video games? Because they're lazy and want the fun brought to them in an easy to absorb and palatable manner. You may not notice this downside at first, but as you sink more and more in to the Wii, you'll find that she's not as fun as you'd originally thought. Turns out that's not an oversized clit. It's an undersized penis.