I've done P90X for the past 2 years. Well, I did Power 90 first & then transitioned to P90X. It worked amazingly! I lost 30 pounds. gained muscle and endurance. I never looked this great before, even in high school. Sadly, I've lost much of it now b/c of my back issues so I've had to really modify. I'm still in shape but I don't have as much as the muscle mass I did before and my core isn't as strong.
Once I get the ok from the doctor, I'm hitting P90X hard again.