The one thing that the MMOGs of E3 almost all seemed to share was a desire to include content for players that has some meaning. No-one has taken that to heart quite as much as Blizzard though, as the large crowds surrounding the plethora of World Of Warcraft machines proved.
Every quest in the game has an associated storyline, often containing multiple parts, meaning your character progression is as much about exploring the unfolding narrative as it is levelling and numbers.