Like Darkshore, Arathi, Silithus, Uldum, Vale of Eternal Blossoms, they added new, current content to existing zones to further the plot. And also destroyed Teldrassil and Undercity, but that doesn't really count.
What other zones would you like to see revisited?
Personally I really want to see an update to the Plaguelands. One restored and blessed by Alliance druids and paladins, one blighted to all hell by the Forsaken.
Another zone modernized by goblins (or gnomes this time) like Azshara would be cool...