Fantastic fitness aid... seriously!
The only small problem is that the songs are limited so you have to BUY - unless you are comfortable in modding the game - fortunately there is a whole community out there who have mapped songs AND utilities to make it as easy as possible for you.
BUT mapping is way hard for a novice - you spend more time on mapping IF the songs you want to work out to are not listed/ not available and more frequently they are not mapped at your difficulty