I got insanity from a friend, along with P90X. P90X seems to be a good way to prepare for insanity..it focuses more heavily on resistance training. I have looked at both programs but only started INsanity so far.
I'm almost through week 5 of insanity delux package and have had super results personally. I notice I'm stronger all around, in better shape,..etc. It focuses on strength building, cardio, balance and flexibility in every workout so you can't go wrong with it, especially if your starting from a sedimentary lifestyle.
As far as weight loss, I don't have anything but a few vanity pounds to loose...I'd say i'm right at %10 bodyfat,..so by the time the program is over I may be leaned out even more. When I started the program I was 150 pounds and now I've accidentally dropped to about 143-144,..but I'm maintaining my muscle mass well.
Month one is fairly difficult,...month 2 has been a ram-rod straight to the gut. You HAVE to exercise where its cool or even very cold in order to not over heat and sweat too much. Give yourself plenty of room and drink water as often as Shaun T. tells you to. Sleep deprivation will kill you on this program,..gotta get your 6-9 hours or else your legs will just drop out from below you.
Here's one problem. You will do a lot of jump training in this program which is out of fashion, but it WORKS. Be careful not to jump on concrete..have carpet or an exercise mat and high quality cross-training shoes. Running shoes are not going to give you enough support. I am working out on concrete and my knees and feet are giving me problems now..I have to take some time off or wait until have a better workout environment.
Bottom line, you will feel like Bruce Lee in a few weeks but watch the jumping.