Another topic that may have already been addressed so my apologies if that is the case.
It would be great if each class has a guildhall with guild masters that gave out quests for the class and allowed you to climb up in the guild as you leveled and learned more about your class. There could be guildhalls in various cities so you could progress (i.e., after finishing out class quests in one city the master could give you an introduction letter to the guild master in a different city. Obtaining higher levels in the guild could open up special orbs, guns, bows, etc. that were limited to certain ranks in the guild.