Michael Esco, PhD, CSCS of WebMD posted a review on Insanity. Here are some snippets.
The Insanity workouts are highly intense and designed for people who are already in good shape. It is not intended for special-need populations, such as cardiovascular, pulmonary, and metabolic disease patients, diabetics, or obese people, and people with orthopedic limitations. If you are extremely unfit and looking for an “easy fix”, then Insanity is not for you. The program will work best for people who already exercise on a regular basis and are willing to work hard.