When ArenaNet set out to design the character classes for Guild Wars 2, they didn't look at other MMO's for ideas. Instead, they drew their ideas from class-based shooters like Team Fortress.
Most MMO's feature the same "trinity" of roles for players. You can either heal allies, kill enemies, or "tank" (i.e. distract enemies and let them beat you up while your teammates do their thing). Rather than designing, say, a healing class or a damage-dealing class, ArenaNet decided to have all of the GW2 classes capable of filling all these roles in some way.
"I just detest dependency and the lack of teamwork it creates," GW2 designer Jon Peters told PC Gamer. "It seems awfully silly to get people to play together and then not have them interact other than to say 'are you doing your job?', 'Yes, I’m doing it.'"
The real difference in the GW2 isn't their role, Peters says, but how they perform it.
"No-one would tell you that everyone in Team Fortress just does damage,” he says. “No one would say a Spy and a Heavy are the same because they both do damage – they’re very different playstyles. They have a very good sense of purpose."
GW2 will be released later this year. You can secure access into the upcoming beta events by pre-purchasing the game.