I've tried some games on it at my local gamestop store. I tried a few sports games, and it's definitely fun to control the game in such a unique way. One of the games was a racing game (all terrain) and you had to hold the controller with both hands and twist it left and right like you would a steering wheel. It takes a little bit to get used to it but it definitely gives a more "authentic" feel for many games.
As much as I liked the controls I'm not sure I'm sold on them. I tend to like a more tangible gaming experience and if I really wanted more realism in a racing game I would just get a steering wheel. I have the feeling that I would get tired of the controls pretty quick.
Now the Wii definitely would be fun for kids who might like the fact more than adults that they can "be" spider-man as they control the character (for isntance for spider-man to throw his web you have to motion the controller in the way he acts, so it's a great pretend!)
For myself I would definitely get a PS3 or a XBOX 360 but for kids it might be worthwile to consider the Wii, on top of that it does play gamecube games (even my wife would love to be able to play Luigi's Mansion since she's a Mario freak).
