I like the increased display size, better graphics, and not having to click furiously to get some pieces of loot that are lodged under mobs, but all in all, the classes seem too homogenized. Sorry if this has been posted 1,000 times before. I just needed to vent. I bought D3 two weeks ago and am burnt out. Normal/Nightmare/Hell all seemed like the same difficulty, then I hit a brick wall in Inferno before I geared up via the AH, but the content just seems... lacking. I liked that a Paladin was different from a Druid was different from a Sorceress was different from a Necromancer, but in D3 the feeling I get is that they're all pretty much the same. Ranged is ranged, melee is melee, and the talents, well... I miss the talent tree of D2. I am not saying that the game is awful, but after waiting for like... 3 years, I feel a bit disappointed.
Edit: I do like the AH, that was a nice addition. I like the online only, assuming that it actually does prevent bots.