I thought thought this was going to be just another workout video type thing that I'd give up on after a week, but I have to say how wrong I was!
I had been using the fitness software that came with the Wii, which was fine, but a bit slow and too easy to wimp out on.
This is completely the opposite. You set the type of workout you want to do and the duration and even the music you work out to and then for the next hour, or whatever, the trainer puts you through your paces. No long pauses, no irritating 'encouragement', and no wimping out. There's a handy countdown timer showing how long you have left, but it cleverly fades in and out with each new exercise so that you don't clock-watch.
I'm already noticing a difference in my own fitness.
The only things it loses points for are that you can't keep track of your daily progress, and some of the exercises require more room that the average persons lounge. Apart from that, highly recommended.