According to most people:
- Captains can heal, but not as good as a Minstrel / RK
- Captains can tank, but not as good as a Guardian / Warden
- Captains can be a melee damager too, but not as good as a Champion
- They can do the roles of many classes, but they are not as good as that class itself
- Their buffs can match up with the debuffs made by a Burglar / LM
- When you have a captain on a fellowship, your chances of success in an instance is increased by a small percentage
That's what I heard about them