From what i've seen and heard, i'm excited for the new look of some of azeroth's old regions. After leveling and playing each class starting area in the same old places as well as the later zones and not exactly welcoming having to do them over again, it will be fantastic to play the new races in a completely different zone, as well as the old classes where i can go "let's create a new character, my favorite class to play and go to this brand new area or even, heck, im going to this old region cause man.. a huge canyon? sweet! and one where i'm not going, "of course the item i need is on this mob in this exact spot in this zone." Even the mobs will be different so i won't have any idea where a certain mob is for a quest line, i actually get to explore and see the sights again. Even then however, those same old mobs, will have more appeal to go to when i know the whole area has changed "man... where did that old pool go that this npc used to be next to, that was my object marker!? well cool!"
I am also excited for the new professions. haven't had one of those in a while! something new! So there will be more things to do, and more things to discover, which for me will make the game much more appealing.