The Wii Fit "game" has four sections.
There is a yoga section, in which you stand on the balance board and it measures your success in holding the position for 30 secs-2 min (depending on the pose) by tracking your center of gravity and stillness. Some poses are easy, some are super hard. I think a yoga class would be more beneficial but it is a fun way to do it at home.
There is a balance games section, which I feel is the least like exercise, but balance is a good thing to work on for other reasons...like simply not walking into things like I tend to do on a regular basis. It also helps you with posture, which makes you look better anyway.
There is a cardio section, with things like jogging in place (or back and forth in range of the sensors), hula hooping (which I thought was pointless the first time I did it for 2 minutes, but now that I do 10 minutes, you do work up a sweat!) and step arobics (basically like DDR).
Then there is the strength section, which is push ups, situps and body resistance exercises. At first I wondered if these would be helpful, but oh, yeah, you feel it in you muscles. Also, I discovered the military trains almost entirely by using your own body weight against you, so its obviously effective.