He talks about it in his book, which is surprisingly a good read (though it's half a body building guide too). A lot of people thought he bulked up and got bigger when he became The Game, but apparently he just got ripped.
I always liked HHH as The Game. I think he plays a very menacing and convincing heel and has put on some of the best main events in WWF/E history. He gets criticised a lot for using his poliitcal power to get his spot, but he paid his dues, worked very hard and I've always believed he earned it.