One of the most important aspects of any MMO is the creation of a deep and immersing world. One of the difficulties of creating a shared space for players (as opposed to a limited single player environment such as Morrowind) is allowing each player to feel like an important piece of the greater storyline they are a part of. This is at the core of the engaging lore in the World of Warcraft, as players do great things during their stay in Azeroth. As one player on the US forums suggests:
I, Cocles, have killed Onyxia; I have killed Nefarian. I have dumped both of their heads at the Warchief's feet, yet he still doesn't know who I am when I show up for later quest lines done in BC. Why doesn't Thrall recognize me as the slayer of Onyxia? He who defeated Nefarian!!...Thrall should know me. Thrall should be glad to see me.
While those of us who have achieved exalted reputation with some of the new BC factions have experienced some of the new dialog, many players have yet to experience the joy of the love of a gnomish skyguard officer who happens to need more aether rays. It seems that these great moments of immersion are simply a taste of what's to come in the future of WoW, as Kisirani on the US forums tells us:
The ability to do it is there, and as we've demonstrated, it's something we're interested in doing.
