Something that Blizzard does extremely well, but goes uncommented on by most people, is the naming system for talents and abilities. The names for each class are extremely well-chosen, and do a superb job of reinforcing that class’s identity.
Take rogues, for example: ambush, mutilate, backstab, rupture, garrote, sinister strike, crippling poison, hemorrhage. Brutal, guttural words. Words which are perfect for the rogue.
Paladins have might, wisdom, justice, crusader, light’s grace, avenger's shield, vengeance. Blessing of Kings. Again, the words used are chosen for deliberate effect, reinforcing the class identity.
Warlocks have corruption, doom, agony, immolate, drain life. Words that evoke the dark nature of the warlock.
You can see similar effects for all the other classes. Attention to details like these is what makes Blizzard games so polished, and their Creative/Naming team has done an outstanding job with ability and talent names.
It's one of those things that I never really thought about, until I saw a different game which had just terrible names for abilities. That made me realize that coming up with good, solid names is not as easy as it seems, and actually goes a long way to making your game shine.