I have the wii fit, and personally LOVED it! However, my board started to play up after a while as I just light enough to use it, so when I did the obstacle course where you have to jump, it would turn itself off, and it became SUPER annoying. But, I did still use it to weigh myself.
Since I have been on Slimming World, I haven't gone near it, I would rather go for a walk or to the gym - dependent on how comfortable you are doing that.
But an amazing alternative (if you have an xbox) is the kinect accsessory you can buy for it which is a sensor/camera so you dont have to use a controller, it just sees you, I have been using the YOUR SHAPE Fitness Evolved on the xbox (but you have to have the kinect accsessory for it to work) and it is absolutely amazing!
No worries about the board, you can move around freely, the only thing is you need quite a large space (around 6ft from the tv) to be able to use it. But on the Your Shape game it tels you how many calories that you have burnt, and so far I have burnt over 1000, and yesterday I burnt 200.
I do love the wii fit, but I did get bored with it, and like I said had a problem with the board after a while.