I have read that for a complete overview of Mike Mentzer's Heavy Duty System you should read Heavy Duty II and High Intensity Training the Mike Mentzer Way (as suggested by John Little - Iron Man magazine). I own and have read H.I.T. The Mike Mentzer Way. Do you know what Heavy Duty II covers that Mentzer's final book (H.I.T. The M.M. Way) does not?
I'm not sure why that was said because H.I.T. The Mike Mentzer Way is fairly comprehensive, but I think it good to read more then just one of his books because he says things in different ways in each.
But I think what is missing from books, like how to do the exercise, correct rep speed, what is failure, etc. is better covered in video form.
If you don't have the Mike Mentzer workout video DVD, it's a must have, it's like having Mike as you own personal trainer.