Vanilla gets a 10/10 for being such an epic game for the year it was released. for me it was a mind blowing game.
BC gets a 10/10 also for improving on the game and for keeping it epic.
Wrath gets a 9/10 for being a great game took the environment to a whole new level and gave a truly one of a kind experience.
Cata gets a 8/10 for taking so much time to revamp the old world and to add new zones. Only thing lacking was the fact that it felt like it was smaller than before because the new zones were hidden areas in the old world. Most of the work got spent on 1-60 IMO.
Mists gets a 9/10 for adding so much and for taking the time to put in such beautiful landscapes that we had to experience on the ground and it was also breathtaking from the air.
So overall wow with the xpacs gets a 9.5/10 in my books it is a truly phenomenal game that not only allows communication with others but allows them to experience the world together as a team like a true MMO should. The amount of work they put into the game is unparalleled and it also allows players to choose their own play style and leveling paths. The players truly have control over their destiny.