My view on what is new!:
Time:
It is much faster to get to 85 than it was to get to 80 or 70. I leveled in a little less than 23 hours i think, with the struggle of people everywhere the first few hours. Server first was after 9 hours (so it can be done really fast). It doesn't feel like it will be a hassle to get your alts up. It will be like 2 day thing to level an alt if you dont really rush it. I like this.
Questing:
They have changed style of how you quest. Instead of coming to a town and gathering 15 quests and then going out to do them, you get 1 to 3 quests that are either chains you can complete and get a followup on without returning to the questgiver (new feature and very very handy), or that you hand in very closeby to where you did the quest. There is more of a storyline, and things phase around you as you complete quests. This they have done to ALL questing in Eastern Kingdoms and Kalimdor, so leveling to 60 is a completely new experience. I really like this.
Zones:
The 5 new zones look good. The underwater zone is probably my favourite in terms of look, but it can be such a hassle to be there. Things arent just east west north or south, they are also up or down. It can be very confusing, i have a feeling Ingek for instance will be lost eternally in that zone.
Questing in the new zones:
The quests are really cool sometimes, and often you get little videoclips when you hand in a quest (with yourself in it!) of what happens next. I like the clips, they are fun, and they make me who dont often read the quests that well or care about lore be a bit more into the story. I think most of the new quests are good.
Dungeons:
I haven't been to any of them yet! They seem hard because people are wiping when i listen
Gear:
Top WotLK gear is worth nothing on level 83 already. Don't think that greens wont be an upgrade and vendor it without looking first. Greens are massive upgrades, and questing at level 83 and 84 is really hard if you haven't upgraded your gear.
Healing:
I have understood from ventrilo that healing has changed. It will not be a spam contest anymore with everyone in a raid/dungeon healed to top at all times. It is going to be a struggle with mana, at least in the beginning of the expansion. I haven't healed though so i'm not entirely sure if this goes for all classes at all times.
That's all i can think of right now.

I really like the expansion!