I really think the Cata questing so far is the best it's been in the game. It is different though, and could certainly be improved upon even more.
Briefly, I like that quests tell more obvious stories about the world now, without the story needing to be inferred by piecing together disparate quest texts with out-of-game resources. I won't say that the quests tell *greater* stories than they did before, but they do tell them more clearly. Also, it's nice having the feeling that you're never out of quests and scratching your head trying to figure out where to go to next (but to be honest, that matter was really fixed with BC).
However, it's sometimes a drag feeling like you can't be a free-spirited explorer wandering wherever the wind takes you because you're so beholden to your "hero" duties. Many of the most memorable moments for me while leveling this character (my first one out of a starting zone) came from travelling the vast world with the wind at my back and only a few mere trinkets to carry along with me.
I remember a particular quest I happened upon in Stormwind that tasked me to go all the way to Stonetalon mountains (low enough level that I didn't have a mount yet, and long before Stormwind had opened its own harbor). Back then I was able to think for a minute and say, "sure...why the hell not? I've got nothing better to do!" Then I picked up my bags and disappeared into the wide open world. I had just recently joined a small leveling guild, had no knowledge of TS or Vent, and this was my first MMO, so when I blazed off Westward into the sunset it felt like I was really, actually separated from the friends I just met. It wasn't quite as easy to just apparate all around the world back then.
On the way to my quest destination, I met a few people that had additional quests I could do and I helped them out locally (like some stuff in Astranaar and the Gnome overlooking the Venture Co. mine). By the time I finished the first quest I started upon, I had leveled a few times (so when I got back to the city I could learn some new spells) and managed to fish up a Blue Sapphire which eventually made me the money I needed for my mount another dozen or so levels after that even!
So, while I think Cata has been pretty awesome in the quest department for what it has intended to do, I do think (and have said before) it's a bit too linear. Some of the whole concept of being an *adventurer* has been lost, when everything tells you exactly where to go next, and when where to go next is right next to where you already are.
I think a good thing to consider for future expansions and games is having people get early quests that direct their character to a far away place or some far away mission, but that literally *cannot* be completed until other steps along the way are accomplished. It would be nice if the player knew what the destination was beforehand, and let the journey be a surprise, instead of the other way around.
An example I can think of off the top of my head would be in the new version of Darkshore. Say, when you get there you're given a quest to help Malfurion close the twilight portal. But there's no real other direction, and you're clearly not powerful enough to do so yet (the quest could be red and specify it's for characters that are level 18-20 when you're only level 10-12). Along the way to get to Malfurion, you run across other quest hubs with people that need help. If you help them, you wind up getting both more powerful, and enlisting the allies you need to help you and Malfurion both (like the Ancient of Lore and the Furbolgs). Instead of each quest hub sending you to the next one like some cosmic coincidence, you're driven onward by the fact that the quest to help Malfurion still isn't finished yet, so you say your goodbyes and wander off again.
After all, Frodo knew pretty early in the story that his real quest was to toss the Ring in the fires of Mount Doom. And while I think there is the obvious overall goal in the Cata expansion to "stop Deathwing," it's a bit too abstract and distant for that to really guide people to the next place they're supposed be and make them really feel like they are an Adventurer.
That's just my 2 cents :)