The thing I'm really looking forward to the most is to return to all the old lands, and be able to fly and see them. It'll be a shame to not see them NOW flying, but at least have an idea. Fly over Stormwind would be awesome. I've ALWAYS wanted to click the huge bell in Booty Bay. I remember seeing someone do it in Live, before BC, and I've never been able to do it, even after trying for hours... I know just wanting that is kind of dumb, but it's always bugged me to do.
Heroic Dead Mines. I'm sure everyone wants to do this too, and they should. I used to run Dead Mines before BC from the level I could, until it was all grey to me.
The graphics. Each game set has gotten better and better with the graphics. I'm not talking about how "good" they are, more so how cool they look. For example the Fire Twilight Ascendant. It just looks amazing. Also how much more intricate the builds are becoming.