It really REALLY depends on who you talk to. Some wax nostalgic about how vanilla was so much better, how change is bad, et cetera... The changes will take some time to settle, but overall I'd argue they're for the better. The account wide changes are actually quite welcome. As for specifics, I mostly play a shaman and while jarring, the new talent system let you play a bit more "as you like/as you need" and less "you have to take talent x or you're bad".