Brilliant fun first time, gets old from the third time on it.
Wii Fit was great at the start. Fun games and the exercises weren't too hard to start with. It's fun to try and unlock about half of the games but after that it just gets boring.
The balance games are fun but due to the limited options, get old quickly. Same with the aerobic exercises with the exception of the free stepping and free jogging. You can go at your own pace while watching tv, which keeps it from being very boring.
I actually find the muscle exercises a little worrying. Having pulled muscles while under the instruction of a trainer, I am very wary of doing it myself. Some of the exercises should not be undertaken by someone following an animation!
Overall, Wii Fit is not worth the large amount of money that it costs.