I think they did an awesome job at quest design in Cataclysm. At least the first time I levelled an 85.
The second 85 was less enjoyable, too much the same, and I noticed how hard it is to quest with a friend unless you started the zone together.
After doing a few more 85's, I decided that the whole "one long quest line per zone" thing is nice and allows for good story telling, but that it's also restricting - you have little choice in what you are going to do, and that's a shame. The quests themselves had deliciously few long pointless travels, though. I hope they'll transfer to a system where there's more branching in the quest lines, but keep a large overarcing story for each zone - I really liked the dwarf wedding story, for example, but I would have liked to have seen some branching off at certain points in the story. Perhaps they could have let each branch lead up to a daily quest as a reward.