I'm about 1/3 of the way through Icecrown quests, and so far, it's one of my favorite zones. Without too many spoilers, here's the gist of the zone.
You get sent out to the zone from Dalaraan. The one-way flight they give you puts you on top of this giant flying ship that circles in the eastern part of the zone. They then send you to this one area to start all the quests in the zone. As you complete quests, more parts of the zone become populated with NPC's you can get other quests from. Along with that, there's daily quests that open up as well.
Think of it as Isle of Quel'Danas, but instead of things opening up when the server completes a certain number of quests, things open up when you complete a certain number of quests. The whole zone has that phasing thing, so there could also be a ton of people in the same area, but they won't be spoiling the quest line for you since you can't see them.
So far, it's a very interesting story of how all of the landscape changes. One of the quests has you heading all over the place (Moonglade and Shatt) to save somebody. It's a fun diversion (and they provide portals for you).
My favorite quest, just becaues I found it to be quite different is also a daily quest. King of the Mountain has you get in this robot, and you jump to the top of the mountain to plant a flag. It's also a PVP quest, so there's horde trying to do the same thing. Here's some hints. Don't worry about falling, you don't take fall damage. Also, you don't have to jump onto solid ground, so just jump onto the side of a mountain and then jump again before you fall too far. You can get to the top in a matter of seconds if you scale straight up like that.
At any rate, I hear there's also a movie, so I'll continue questing there so that I can see that. I still haven't replaced much of my gear at this point, but I'm slowly starting to. I went straight out there at lvl 77, so you don't have to wait until 80 to go out there. And the zone is basically designed to be used with a flying mount, so that's nice as well. There... there's one bonus of Cold Weather Flying. lol.