The graphics in diablo III look prety awesome.
1. Where as in D2 your enemies died in rather predictable ways, in D3 they will die in every way from melting in a ball of flame to having their body parts sent flying across the room.
2. Where as the graphics in D2 were stupidly overdone to the point of being plain silly (durance of hate in hell, I doubt the whole population of earth could have that much blood) D3 seems to be much more eye pleasing and provide the looks one imagines on a quest to stop evil.
3. In D2, other players did not show their equiped gear if the gear was carrying itself. In D3 you will most lilkly get to see everyones gear in full glory and not some "nacked" hammerdin dealing stupidly high damage with max block and enigma.
The only complaint I have is with the trees. I guess they were done that was to keep requirements down though.