Guild Wars seems to be a mission based game, wich is quite different than other MMORPGs. In other games all you needed to do was get a group and kill the same monster for a few hours.
Guild Wars will make you take on a mission with a group, it creates a dungeon for that group only and when it's done well... it's done. I believe it will be a lot easier in this game to stop whenever you want.
I'm not sure if it really is going to be good, so I'll try it tomorrow and get a good idea of how the game works. I'll be on it tomorrow at around 4pm est. My name will be Rythok, just in case you cross paths with me.