Well, I'm excited about more than one thing, but if I had to choose two of my fav, it would definitely be the more in-depth Quests and Radient AI.

I'm getting more excited about the Guilds as well, after checking out the official ES forum-topics that has info on some Guild quests. It seems that the NPC's will more at least more interesting, and have more personality than Morrowind's.
(However, I'm worried that only a few NPC's will be really deep, and the rest of them would be bland, like in Morrowind, and I hope that would not be the case. Also, I hope the entire game would not revolve around dungeon-monster-fighting
entirely. I prefer fighting outside, not inside scary, dark places.

)