For someone who has worked out for more than 15 years, I can honestly say that in the hands of a dedicated individual Wii Fit could really change their body ... and it is accessable enough that some people who are not motivated by other forms of excercise may become highly motivated to use it.
With that said there are a lot of minor problems, a couple of more major problems, and some missing features which prevent this game from being as great as it could be. In particular, menu navigation and the results screens are too time consuming and limit your ability to get a really good workout, the Wii Fit Channel should have been opened up to enable third party developers to create games which take advantage of it (DDR comes to mind), it could have really used a custom workout mode where you could program your own workout and run through it (without menu navigation), and downloadable content could have kept the variety high to help people remain motivated.
Now, even with its problems I would still say that Wii Fit doesn't suck.
