One thing that has really impressed me about WoW is the Racial Cultures.
None of them seem to be just "whipped up on the spot to fill a niche". Each one is a seperate culture, each with it's on specific history.
But the one that impressed me the most, the Tauren's. As you progress as a Tauran, you cannot feel that they are an "Evil" race. They hold honor, love of the land, and balance of nature very dear.
Are they part of the Horde? Yes, but they are part of the Horde because the Orcs befriended them and basically saved them from extinction at the hands of the Centaurs. Because of this action, they feel a strong sense of loyalty to the Horde as a whole.
I have a feeling that if it had been the Humans/Night Elves/Dwarves or the Gnomes that had come to the aid of the Tauren, that they would have just as easily sided with the Alliance, and would easily be viewed as a "Good" race.
But one thing I have noticed, in the world that is Warcraft, Good or Evil is really how each side is conceived by their own standards.
Orcs- They have known nothing but battle all their harsh lives, and finally having won their freedom from the Burning Horde, they will steadfastly defend their new-found freedom to the death.
Undead- Having wretched themselves from the sway of the Lich King, they will bow to no more masters. Humans have always sought to eradicate them from the planet, so they are defending themselves as best they can...and giving it back.
Troll- Always all other hands have been turned against them, but when one tribe was given aid by the Orcs when facing the threat of extinction at the hands of Murloc's they have shown a strong loyalty to the Orcs.
Tauren- Stated above.
So, guess I am just rambling on, but I still like how the quests reflect these cultures.