I would like to see the complete overhaul of the combat in D3 (project D?)
Combat in D2, for me, was mediocre. Some skills were useless, others were uninteresting, no combos, few attack animations, no block, rolling is the only dodge animation. After few hours it gets tedious and repetitive.
So what I would suggest is, customizable skills (Diablo 3) or their combination into more powerful skill (Fable 3, Bioshock 2). Or maybe something similar to Kingdoms of Amalur: Reckoning destinies system. More variety in skills, or less skills but more complex.
More attack animations, perhaps implementing the combo features
Different types of armor, not just metal plates and chainmails.
More complex bonuses granted by the equipment. (for example: Set gear grants new spells that can't be obtained otherwise. More parts of the set you wear, more powerful the spell becomes)
