A few key things I personally am super excited about:
NEW CHARACTER MODELS
10 level increase from 90 to 100
Being able to choose a character to be level 90
For me, the most important are the top four I listed. For social reasons the last one is also important. Being able to have a character become 90 means that my friends who have been away from the game for a while won't have to do any catch-up leveling.
This is just a small skim off the top of the information of what's going to be included in the new expansion.
When I have more time, I will post more on the top four in my list of reasons why I'm super, SUPER excited about this expansion.
FOR THE HORDE!