Overall I'm pretty enamored with the new zones and quests but I did have a few notes and concerns about the current design:
Being unable to access new starting zones. When I do recruit new people to play the game, or when starting on a new server it is pretty standard for me to hike over to where the new player is starting. While this is understandably difficult for a level 6 to do, I believe it shouldn't be impossible (especially for my level 80). With the new goblin starting area erupting and disappearing from access forever, my friends would have to level to at least 12 before I could even get to them. This takes absolutely forever when they are brand new to the game because they are still learning how to navigate the questing system etc.
The linear questing system frowns upon skipping green quests. I really appreciate the enhanced storytelling you get from the very linear questing system, however it makes me very hesitant to drop quests when I start to outlevel them. This problem is compounded by the presence of rested xp and heirlooms. I find myself leveling much faster than the quest flow intended and very hesitant to try to jump into a new zone, not knowing where to start. I have not really been doing dungeons, but I assume if you can get half or a whole level in one at low levels it throws off the process even more.
Too many minor quest hubs lead to a lack of stopping places. In the old style of questing you would get most of your quests from a town, so you could go out and do a few quests and when you returned there would be an inn, a vendor and a fp. Now you frequently get a fp and probably a vendor, but inns seem very hard to find. A perfect example of this is Desolace where you can quest for 30+ minutes without making it to an inn. On alts I often level in small spurts while waiting for something to happen, so I like to be able to log off in an inn right after I turn in my quest.
An abundance of vehicle quests cuts down on grindy xp. In thinking strictly of xp per hour vehicle quests are generally your worst nightmare, even though they may be fun. Right now they give the same xp as a "kill x" or "gather x" quest, but you don't actually get xp for killing anything while in the vehicle. So essentially you're not getting as much xp for 2-3 minutes and sometimes these vehicle quests are strung together so you might not be actually killing things for 10-15 minutes. I dread these quests especially if they are relatively difficult vehicles or don't kill things faster than my character could. A couple of examples of these quest chains are the reprogramming of the shredders in the beginning of Azshara and the air jousting in Mount Hyjal. I think this could be solved by simply bumping up vehicle quest xp a bit.
There are two continents, but there is no real incentive to visit both while leveling. There is certainly an advantage to cutting down travel time while leveling, but I used to really like going from durotar to the barrens and surrounding zones then maybe some Thousand needles before heading off to Stranglethorn Vale. I also rarely missed an opportunity to do Arathi Highlands, the Badlands and the two Plaguelands. But now there is no real need to go over to the other continent (and while I haven't tried to do a full EK run yet, I assume it is similar there).