I thought Insanity was awesome. I did the 60 day rotation they suggest. My cardio capacity improved greatly (and I thought it was pretty good before I did this series), my legs got stronger and my upper body (mostly tris and shoulders) got stronger and more defined.
These are my favorite workouts of all time. I really like the drill style of working out and the way he does it without the traditional rests. I thought they were well put together to keep you challenged from a cardio and a strength perspecitve (although they are mostly cardio workouts).
For me, the straight ab workouts and the recovery workouts in this series were unremarkable. I wouldn't judge this series based on Insane abs. Do the meat of the program, the cardio workouts.