It is very different then any other Mmorpg I've played.
1) Promotes Teamwork. I feel like they actually promote teamwork more then other MMORPGs.
2) Promotes Responsibility. Everyone is responsible for there own health.
3) The players. A heck of a lot less rude players/trolls/elitists in this game.
4) Freedom. Almost every aspect in GW2 you have a choice to change. Crafting/Weapons/Spec/Questing
5) Invisibility Option. Sometimes I make friends with people and realize I shouldn't have. So for a softy like me becoming invisible is a huge plus. Sometimes I like to play by myself.