UpTheMiddle nailed it-- cardiointensive, not much resistance training, less time commitment than P90X. No perfect system out there. P90 has almost no cardio except for plyo (the kenpo punching/kicking doesn't get my heart rate past 130). The time commitment is much less for Insanity, but there is minimal resistance training and not nearly as much muscle building--look at the students--the women look like skinny models, the men mostly look like cyclists. Most P90 programs are about an hour, and the yoga one is over 1 1/2 hours. The followup P90X products (10 minute work out, P90X2, etc) just don't seem to be as addictive as the original. The P90x ab workout is still the best I have found--"He's making contact! He's making contact!"