I didn't try insanity, but I looked into it a while ago, so that's just a general opinion ... if you're the lazy type (and I was too) this is going to be tough to keep up
I started working out again 10 months ago after 3 years of doing nothing and it's way easier if you sign up for a local gym with a buddy and the two of you can motivate each other to go regularly. Also creates a little "competition" (you don't want to lift less than your buddy, do you? ;) ). Now after 10 months of going to the gym 3-4 times a week i feel bad when I didn't go for 2-3 days - so I guess now I'd be able to push myself through something like insanity, but at the beginning I'd have done a few workouts and then put the DVD in the shelf.
If you're looking to burn a lot of fat and gain some muscle you could also check if there's a crossfit-box in your area. These guys really push themselves and get great results without heavy lifting or boring long-time cardio (e.g. running for 1 hour straight ...).
And of course watch your diet
