Gameplay changes are welcome. I am intrigued by the addition of rated BGs. It would be nice to bring back some of the risk and competition of the arenas back into the battlegrounds. I welcome simplification of stats - at the moment, people have to consult spreadsheets to balance defense and ArPen in particular. I am quite indifferent as to the new races - I have been a night elf fan from day one, and what I can't get as a night elf, I get as human. Neither the worgen nor the goblins pique my interest.
As an RPer, I am absolutely livid about the lore changes, particularly Garrosh leading the Horde (what the heck was Thrall thinking, appointing him leader?), Thrall becoming the new Guardian of Trisfal, and the loss of Alliance territory to the Horde (Ashenvale, Darkshore, Southshore). I am, of course, an Alliance patriot, but these changes really should be questionable to anyone.
At the least, it gives my characters even more of a reason to hate the Horde and take the fight to them. You can bet I will be spending more time in BGs and less in the arenas after this expac. ;p
EDIT: Night elf mages exist - the Highborne - think Shen'dralar. They would be rather rare, but they do exist.