Some of the additions offered include a new race for both sides of the fight, the Blood Elves for the Horde and the Draenei for the Alliance, each with a whole new set of storylines, capital cities, and a brand spanking new continent. Additionally, these new races bring complexity to the war, as they are both traitors to the other side. The expansion also offers more enemies and allies for each side. Finally, Horde can now play as paladins and Alliance as shamans.
Furthermore- my favorite trait- players are now able to Look for Groups doing the same quests. Other expansion characteristics include expanded talent trees and new professions such as jewel-crafting, and the removal of the fairly useless (to me) honour system.
Why am I, whose main is only level 16, so excited about an expansion that is mainly geared toward lvl 60 players, with new quests, zones, mounts, and instances reserved for these high-enders? I guess part of it the knowledge that at some point I will indeed be one of those crazy nerds. The other part is that I love the idea of being able to do quests in groups easily. But finally, I so badly want to play as a Draenei, who crashed their spaceship and who you begin play as surrounded by the wreckage of your ship and the corpses of your comrades. Awesome.