I think it highly depends on what games you play... four modes/categories of game:
1. Balance - not likely to have any impact, although the ski jump is quite fun
2. Yoga - again, probably no weight impact, but if you enjoy it, it's not bad for stretching
3. Strength - obviously all body weight based, I don't see a whole ton coming out of this - just go to a gym
4. Aerobic - if you do the extra long run (15-20) it's not a bad warm up, and the extra long hula hoop can really kick you ass, but in terms of activity that will shed pounds... that's a lot of hula.
Overall I think it's a motivator and fine to maintain weight/activity if used enough, but to actually lose weight, I think it's a stretch. Still, it can be fun.