And while I was waiting until the event completely ended to do a final analysis, Colin Brennan over at Massively isn't waiting -- he's got a good analysis up over there about the zombie event and just why it was so brilliant. He describes how the world event not only gave players a terrific reason to hate Arthas enough to go to Northrend and want to fight him, but how the gameplay design of the event (when you are killed by a zombie, you become one) was tuned towards fueling the story and the immersion. As he says, the best way to fight the plague was to embrace the fact it was in the game, whether you were a zombie or a cleansing Paladin.
There's lots more to dissect with this world event, including how Blizzard brilliantly invoked something that had happened by accident -- the Corrupted Blood plague -- and incorporated it into the game itself, and how the various zombie abilities were aimed directly at gameplay only possible in an MMO, from the AoE healing to the shrinking plague incubation time. I'll go so far as to say it expanded the boundary of what an MMO can do -- Blizzard let zombies loose on the populace not by hiring GMs to run around on every server, but by giving power to the players. But again -- there'll be time for analysis later, once we've discovered ingame just exactly what's going on here and how it all ties to Arthas. Colin's analysis is a good start, though -- Blizzard really outdid themselves with, even considering the complaints, one of the best world events ever seen in an MMO.