D2 was just a better ARPG experience. Forget all the end game crap or PvP nonsense. I liked the music, the art styling, the classes, the monsters, the itemization, the atmosphere, the creativity.
If D3 went the in depth skill tree route, with a stronger loot system core, it would easily smoke diablo 2 for breakfest.
D3 did a lot of things amazing, but some key things like the loot it was way off. They are addressing in the expac and blizzard has my money.
Better skill system, much better itemization system, an art direction in a more Diablo style, a better music score, better classes and if the game actually had some heart and atmosphere then maybe it would beat D2.
Only improvements I have seen in D3 is the combat and gfx quality down to it being made on a much more modern engine and some other little things like auto gold pick up and shared stash. I actually feel like D3 has devolved to a hack n slash pre Diablo more akin to Gauntlet.