I'm looking forward to the new races of course but also the changes being wrought on the old world and the re-ignition of the Horde/Alliance hatred and of course the raise of the level cap and the new dungeons and raids that will be apart of it. Also to see how the story of the game will progress and evolve.
I have played almost every class at 80 and have raided with them so I look forward to brigning them along to 85 to see the changes to the largest MMO with them.