Part of the charm that the original Guild Wars has is that every part of the game world is instanced in some way. This allows players and groups to jump into their own instance. Players then could avoid contact with other players in the game world, side-stepping things like kill stealing and other types of interaction that could cause one grief. This had its obvious benefits but it also detracted from the massively multiplayer feel and allowed players to be anti-social in a social game. However it looks like Guild Wars 2 is leaving that approach behind in favor of a more traditional instancing model.
While there will be instancing in GW2 it will be reserved for dungeons and also for what World of Warcraft fans would call phasing. Lead Designer Eric Flannum explains, “Dungeons, for example, are instanced areas designed for group play. We also use instancing very heavily in the players’ personal quest chain to reflect decisions that the player has made on those quests.” Flannum also explains that GW2 will be set up more like a traditional MMO where the world is full of players and has a persistent nature, “The game is structured much more like other MMOs, with the world consisting almost entirely of fully persistent areas.”
So in short, GW fans should be prepared to have a more traditional experience in GW2, at least in the way the environments are concerned.