I think im just reiterating what everyone else has said but Its hard to compare these games because of the different genre's however...
AoE is a great game but WoW is in a different league! And the social part of WoW just makes a brilliant game even better (so long as you find nice enough people to chat and play with that is...) And as for the fact that it costs $15 a month. If you bought 1 new game a month, how much is that? Now tell me it's not worth it!