I agree with the balance part and crucible. Balance was the biggest complaint on these forums in D1. But making PvE extremely easy and everything so easy to get had nothing to do with balance. Simple class systems and static rolls made it easy to balance and made it easy for a 30 minute a day player to keep up. So yes balance played a big part, but driving sales to casual players played a bigger part. Remember Activision like CoD sales numbers and D2 got amazing reviews it's first month and it sold a lot because the grind was gone.