Yes and no. Sometimes the things they change are stupid, sometimes they hit the nail on the head, it's a bit of a toss up. Imo Cataclysm was the worst xpack because of the various class changes, destrolock for example went from superbly fun in LK to a chore in Cata (Soulfire buff to be mantained? Fuck that shit with a hot poker).
MoP in my opinion made several classes more enjoyable, even if slightly so, WoD changes on the other hand have completely failed to impress me so far, but it's hard to tell if they'll have a positive impact on gameplay without spending a couple months trying them out.
WoW has something magically addictive behind its combat system, more of the same since 2004 (early 2005 for us europeans) and yet a ton of people are still hooked, hell I'm the first to admit that while I like also other games and other MMOs, WoW is just better and feels like home nowadays.
Anyway, I have a question for some lucky bugger in beta: how is brewmaster doing?