I think you could conceivably lose weight with this game but the amount of calories you burn per hour is pretty pitiful. I would say that at a best guess you could probably burn ~200 calories per hour if you really worked hard at it. By comparison, I burned 250 calories in just over 20 minutes with Wii Sports Active. Clearly this is a much more efficient approach than the Wii Fit titles. I have Wii Fit Plus and use it, but more for the Yoga stretching and core strenght building. I find it a good "off day" program for the rest days in the Wii Sports Active 30 day routines.
All this being said, 30 minutes of steady running is typically worth about 500 calories so none of these games are going to take the place of a serious cardio workout. But since I don't seem to have the lung capacity for a 30 minute session of serious cardio at this time, the Wii games are working perfectly for me.
Good luck and enjoy. Both games are a fun way to get some exercise in.