My wife bought Wii Fit Plus at Costco earlier this week. I think she bought it to encourage me some more. I've been pretty good about watching what I eat very carefully and exercising for at least a half-hour each night on the Wii.
I talked about some of the Wii Fit Plus features over at Slimmify but the biggest overall difference is that this software makes you think. It tests your memory, judgement, and the extent to which you can achieve mental disconnect between different parts of your body. Some of the games are really, really tough, not necessarily in a physical sense but in a mental sense.
It's like walking and chewing gum on steroids.