Great for kick starting a workout regimen.
The best analogy is to think of Wii Fit as Brain Age only for physical, instead of mental, fitness. In the few minutes I played it last night I really enjoyed my time. I attempted approximately seven of the different exercises and while I can already see that they will get ridiculously repetitive I know that that's true for any workout regimen that you might fine yourself doing. The whole point is to help you get in shape. It's not a bowflex or a treadmill or a personal trainer. It's a balance board, some stretching techniques, pushups, etc.
As a new father, I don't have much time to spend focusing on one thing at a time. Wii Fit is quick, easy, and I can pause in between each workout without worrying about where I left off because I can start anywhere without a problem. My fiance is going to use it to help lose those baby pounds and it gives her something to do when she's stuck in the house with the baby all day.
All in all, I'm glad I spent the money on it and unlike many of the other Wii titles this one will actually be used in my home instead of being shelved a few days after buying it.