I finally got in! Happy for me right? The game is still very much in the beta stages; in fact I'd call it more of an alpha...it's nowhere near release and I think in some ways this could harm the game down the road. That said, a few interesting mechanics changes have made it in and I thought I'd talk about: abilities with charges, class specific quest rewards, better leveling curve and passive-active abilities.
Edit: A few extra notes at the end!
So as I said there are three mechanics changes (in addition to the AoE looting which was already announced) that have been kept more or less on the "down low" so far but I thought had a large impact on the game.
Runes: Not just for Death Knights anymore!
Many of the abilities in the game now have "charges" meaning they can be used several times in quick succession before triggering a cooldown; then will regain 1 charge per X amount of time. Hand of Gul'dan was one, with 3 charges initially. The Monk "Roll" ability is another, with 2 base charges. They operate almost identically to Death Knight runes but the charges are limited to that particular ability.
Quest rewards, now always useful!
In my limited experience in the beta questing areas I noticed that now all quests reward items that are somehow useful to your class (if they reward an item). Having played SWTOR for the law few days this was a welcome and comfortable thing to encounter. I always disliked seeking a bunch of rewards that I couldn't use as the result of quests, and it often meant that certain classes had to wait even longer to get to the same level as before.
Softening the difficulty curve
While I certainly dislike the "ROFLSTOMPING!" one becomes capable of at high gear level towards the end of an expansion when one encounters a mob out in the wild and 2-shots them (or less). However in both TBC and Wrath there was this awkward "jump" in difficulty from one expansion to the next. A character hitting level 80 and coming to Vash'jir or Hyjal with a mix of greens/blues from Icecrown or Storm peaks would spend a few levels feeling EXTREMELY squishy; some classes would have trouble taking on more than a single mob. This has changed in Mists; the mobs are a little tougher but they start out at level 84 and the jump is softened slightly. Characters in heroic gear will probably find it very easy, but the curve will catch up as they move into the newer zones. In other words; the zones are designed with new 85's in mind just as much as old.
A new feature, ripped straight out of League of Legends (at least that is where I first saw it) are the "Passive-Active" abilities, which have a passive effect, or can be activated to do something new (usually a more powerful version of their passive) and while on cooldown the passive effect goes away.
I like this primarily because it is Blizzard moving away from the old "push button, something happens" types of abilities; that and it allows them to have fun little effects and additional risk/reward balancing around when the right time to use said ability is.
Well that's it for now, if there's anyone out there not in Beta itching to know anything let me know and I can check! Though currently only the first 3 zones and 1 instance are open.
PS: The character creator female Pandaren icon, clearly we're in alpha:
One major issue I am noticing with Pandarens is that they make other races look BAD by comparison. The pandas are well animated and detailed; stand them next to a human (or any old model)...or even, stick a human on Pandaria...and they just look out of place, it's kind of jarring.