Well, WiiSports doesn't give a good glimpse of what the Wii is capable of. The hardware can support visuals as stunning as the 360, but the whole "Mii" concept is intended to look cartoon-y. If we could create ourselves too realistically some people may get offended!
In the end; it's about the entertainment and you're saving $200-$400.
The Wii is still new, all the games released are to understand how players will react to them, that's the main reason all the video games feel like short mini-games. In time, the Wii will give us excellent games.
I love my Wii, and I trust Nintendo. I also enjoy exercising with it. You don't realize you're exercising because you're having fun. I think that's a major plus for the Wii.
Also, check this out. Nintendo will be releasing a new controller for the Wii called "WiiFit" It teaches you yoga and gives you a schedule to exercise! It will also monitor your health to see if you are improving or not.