Game-pace and animations are beast at d3. Dont change that. What i would love to see is more complicated and tier-ed skill tree. I want to have like few levels of each skill that you can upgrade. Each of them giving something more than a flat % at max level - i.e. whirwlind that for all lvls add %dmg and at max lvl adds life leeching. Move runes powers to unique items and add random roll of +lvl of random skill to them. Thanks to that hunting for good or bis items will take much more than in current setup and it will make mutliple different builds possible. I.e my uniqur sword that gives whirlwind tornados can drop with +3 to my passive skill that gives me damage reduction. On hardcore i take that gladly instead of +3 to whirlwind but on softcore i would hunt for +3 to my whirlwind or dmg passive.
Ehh itemization and skill system is the core. They did gameplay good.. keep it and change itemization / skills