Wii and WiiFit

Well, my husband went and did it. He bought us a Wii and a WiiFit.

Needless to say, the kids love it. I have to admit, I like the WiiFit.

Will it have long-lasting replay value? That's what I want to know. And, can I get a genuinely good workout with it?

Also, I wonder, which games are a must-have for a 10 year old, 7 year old, and 4 year old?