I have this game for Wii, and I did the entire 9 week challenge (on 'Hard' level). It starts off a little light, but it becomes very challenging. It actually got me in good enough shape to go right into P90X without a problem when I was done.
The pros of this program:
Excellent cardio work
Excellent lower body workouts, including a variety of squats and lunges
Excellent plyometric work (jumping activities)
Great graphics and sports themes
Not quite enough upper body work; shoulders and triceps are ok, not enough chest and back
There isn't enough recovery time between days in which you use your legs a lot -- even on the upper body days, you do a lot of lower body cardio; this ends up being hard on the knees (this program was a lot harder on my knees even than P90X is)
Upshot, though -- it is really worthwhile and challenging, and if you complete the 90 days at a high level you can go on to do even more challenging fitness programs. P90X or Insanity shouldn't be a problem for anyone who can do this program on hard.