Gamasutra has a good piece on the upcoming Guild Wars and the need to really make some progress in the mechanics of massively multi-player online role-playing games (MMOs):

"We're finally seeing a point where companies realize that they're not going to create the next great MMO by just copying what's come before," said Christopher Lye, global brand director at ArenaNet, who believes the definition of an MMO has come to mean games that follow a similar quest and combat structure to World of Warcraft. 

"'MMO' is a platform and set of technologies, not a game design model - and we've barely scratched the surface of what's possible ... Honestly, I think the problem is that there's been a lack of change in MMO design and that Guild Wars 2 is a reaction to that."

ArenaNet is also breaking what Lye called the "holy trinity" of MMO combat -- tank, healer and DPS -- and omitting a dedicated healing class all together, giving some healing abilities to each profession. The designers hope this will "free players up from that dependency, so you see a lot more creativity in party make-up and tactics," said Lye.