Of all the changes since the Shattering, three things have stood out in my mind: Questing, Deadmines, Silverpine. These three things are those I have experienced and I will not commment on something I have not yet seen or done, so here we go.
I've done the Human, Gnome, Troll and Undead starting areas. The Human and Undead have some improvements, especially Undead, and each goes by really quickly. The Gnome starting area was cute and had some really good music, while the Troll starting area provided a nice dialogue between Vol'jin and Garrosh but was a bit overloaded with tiki target dummies. All said and done I did enjoy each of them. Perhaps it was only because it was different and I can't see objectively, but I didn't really see anything wrong, I mean they are just starting areas, right?
Questing overall has become compact, orderly, efficient. The new feature where you finish a quest out in the world, can turn it in without going back a million miles to the questgiver and pick up the next one in the chain really adds to the pace of questing and takes away many a long stroll back to the quest hub. This especially becomes prevalent in Silverpine forest, which I'll get to, but can be seen in all areas to different degrees.
A good example of efficient and progressive questing can be seen in the Southern Barrens. You start up north and do some quests bashing alliance forces, then move down to the next camp, then to the next, until finally you reach the Battle Scar at the very south where all the area "PvP" comes to a head and you see the tensions between Alliance and Horde in their full glory. It was a fun trek as no quest hub held me questing in an area for too long, it was planned well enough so that by the time I'm done I've completed the 5 levels the zone is intended you to pass through.
Some may say it goes to fast and an Exp nerf needs to be put in place, I'll leave that argument for others to make. For myself I'm able, for what I've seen so far, to go through a zone and see it's full story (good or bad), from beginning to end. That's something that I've never done before, so in that sense I see that Questing has improved.
I wasn't expecting it to be any different than the old one, as I believed the changes were only meant for the Heroic lvl 85 version. So it was a fun surprise to see the deadmines changed. Quest givers are inside the instance, at the beginning (and appear at the end INSIDE the instance), which makes it convenient for sure. Perhaps the best thing was after we downed the first boss I see in party chat "wtf are monkeys doing here? lol". Yeah, monkeys with pick axes in the Deadmines, it was beautiful to see and absolutely hilarious.
All boss fights are changed, and each one is challenging in its own right. Improved boss mechanics, a little coordination is required to keep everyone alive, and at the pinnacle of it all to see Cookie the murloc jump into his cauldron and throw food at everyone was a sight I shall never forget. Oh yeah, there was a big bad Worgen on the boat that makes everything go foggy...really cool fight.
The changes are terriffic, really a fun experience to go through. Having to dodge cannon balls to dodging loaves of bread make the Deadmines my new favorite low-level dungeon.
Captivating story line, fascinating movtives of the Banshee Queen, a stroll through the ruins of Gilneas city, and ultimately to a bugged quest that killed all questlines in the zone make this my most loved and hated new zone.
What angers me most is that this particular quest that's bugged and stopped my new Troll Druid from finishing the story there was bugged in the Beta, on the PTR, and now on live. You would think that Blizzard would have done something about it considering it prevents people from seeing all the climactic events of the zone, but hey, why worry when you're getting paid, right?
That said, the zone had all the great elements of the new questing mechanics that any other zone had. All the worgen you get to kill really makes you starting thinking that you're a vampire with a human girlfriend that....uh, really bad tangent, sorry!
If the bugged can get fixed I may say that it's the best new zone in the game, but then again there are a couple dozen zones I haven't tried yet so my opinion really isn't worth much right now.
Let's just get Cataclysm rolling already, I don't like this two week waiting period to experience everything. But until then, there is still much to enjoy, to see and to do.