I've experienced all the new zones now, so I felt I wanted to post my (condensed) feelings on them.
I found Vash and Uldum to be the best zones of the expansion in every aspect. Quest lines, atmosphere, zone layout. Both zones are gorgeous and fun to be in, even though one is an underwater zone and the other is a desert.
Both zones also have two awesome human NPCs right off the bat. It's like, they wanted to make it clear from the start which zones were the most awesome ones in the whole expansion.
Next is Twilight Highlands, which is nice initially, but then the quests become a bit boring and the cutscenes/writing really lack a lot of polish. The Deathwings cutscenes lack direction, and there are instances like the Earthen Ring quests, when a troll first talks like a troll, and then stops talking like a troll. Yet the zone is good looking, there is the 300 reference, the gob squad and it's a pleasure to fly around in it, so it's right behind Vash and Uldum for me.
Then there is Deepholm. The zone has nice quests, great quests rewards, some NPCs are linked to the old world in funny ways, it has a sort of variety while keeping its consistency and some really funny lines, like for example the quest where you get to become immune against a certain mage spells, and seeing his reaction is laugh worthy.
There is also Milhouse Manastorm, so all in all great zone.
Mount Hyjal is nice yet not great. The zone looks good, the quests give you a sense of really being important, special, a hero. It is the perfect zone, questline wise, to shut up people that always go "how can a bunch of nobodies kill those mighty creatures?!?!", as the zone makes it apparent you aren't a nobody.
But in the end, I found the zone to be somewhat forgettable compared to the other ones.
It has one of the most awesome looking places though, Ragnaros Seat (I hope I'm remembering the name right).
Last is Tol Barad. I hate this zone. It is the most shitty zone that they could have made for the expansion. I hate it with a passion. It's ugly, packed with annoying mobs and boring dailies, yet its faction is the only one to reward weapons. Playing in this zone for a couple days made me want to tell Blizzard to go fuck itself.
All in all, I really like Cataclysm. The use of cutscenes is a good addition to the game, although they need to hire some real directors, as some of them are really lacking, with bad shots and camera placement.
I'm a bit disappointed by the writing. I've found way too many typos, wrong words in the text and characters talking "out of character" in their text. English isn't my primary language, but there were instance that I'd compare to using your instead of you're, and that stuff really irritates me.
