I personally can't stand them. It's the same issues I have with regular cardio machines: time just drags on. Being in the dentist chair goes faster than 25min of Insanity.
One of the newer ones I did a circuit of, was the Men's Health Anarchy Workout. 30min, similar to Insanity, but a little bit easier (More 10-30 second breaks). You only do it 3 days a week, with some optional 15-min "torchers" for 2 other days interlaced with the main 3 days. I find this works best for me because Weightlifting has always been my go-to, and you really can't do BOTH Insanity/P90x and weight train. Which brings me to some advice: Do the exercise you truly enjoy. Be it running, hitting the gym, or whatever. These workouts should ALWAYS come first. Video workouts will never be my primary because I don't enjoy them, so they are always secondary.