So I've been playing around in the Beta for a few hours now and I love it. Aesthetically, it's just incredible the beauty they've created. Each zones oozes atmosphere and it's really going to be great to see come release.
I've created my Worgen as a Hunter and he's reached lvl9. The whole starting experience grabs you from the moment you step foot into a Worgen-terrorised Gilneas. The art design is, as mentioned, fantastic and the phasing elements change the world every time you turn around. As you near the end of the second area and have been Worgened, you experience the beginnings of the Cataclysm. The previous villages and quest areas become flooded as broken earth juts up everywhere. Fun fun :)
The new Focus resource of Hunters really makes them a unique class now, imo. They are enouraged to stand still more often than not as your ability to spam abilties (as with when having mana) is now not possible since you get two Arcane Shots before you're then out of Focus. Steady Shot (with no Focus cost) really encourages more of a sniping style of play where you move from one position to the next to get a better shot (rather than just run around in circles constantly). I think it'll bring a very unique style of play to the class that hasn't really worked properly until now.
Vashj'ir is somewhere I've only spent 30 mins or so in, but it has this otherworldly feel to it as you float around on the sea floor surrounded by a forest of kelp.
My Moonkin enjoyed his new tricks, but I worry they'll get old fast without the talents and uniqueness to back them up. I'll have to wait until the next build before I decide to panic or not, though.
Moonkin don't float :S
My Warlock, Onaar, spent about 5 mins in Hyjal before I decided that there wasn't really much to do on him since the current build has little change to the class other than the Soul Shard redesign (which is looking great!). While trying to pose and get Arakashak to bloody sit still I discovered that falling from the World Tree will kill you as it's a very long way down.
At least I found that when I res'd, dear Arakashak popped out ready and waiting! It always was a pain leveling a Warlock, dying and then having to resummon your pet. Nice touch :)
I've decided I won't bother testing the other classes until the next build.