Good fun with one major problem
I have discovered through trial and error that actually mimicking the steps on the screen doesn't get you anywhere at all - the character will go green far more often if you simply leap up and down and side to side. This does defeat the object of trying to copy the instructor but does give you a more energetic workout! Unless you can get lots of green and hence earn energy, it doesn't seem like you can unlock other levels.
I do enjoy playing this but it is no replacement for a real class.