My biggest complaint now, beside Crusader sucking, is that certain gems are simply too strong. Green gem in weapon, purple gem in helm. Just too powerful for any alternative to be considered.
It's a by-product of essentially 1-stat system (everything depends on DPS, even hp and survivability), cant be fixed in any way. At least diamond provides some sort of legit choice for helmet/armor socketing for some classes/specs (not me though, i spam forb all the day
).
All the nice little side events, the atmosphere/color pallete, the new enemies, everything is much improved.
Most of them existed before, its just game (via Bounties / Rifts / legendary mats) forces us to actively seek and see them now.
My personal complaint is that gold sink are really overtuned now - one perfect gem requires to spend around 10 mill gold on it, which is fairly big, considering that gold drops have been nerfed considerably (and no AH)