I love playing Zarya, probably my favorite tank. Figured out that when you give your team a shield, that shield buffs you as well. Gonna try for the "Stay above 70 power" achievement. I always run directly in the line of fire (thanks Bastion) and have them charge me up, then skitter away.
The black hole ult is amazing at clearing a group at the payload / capture point. Just make sure theres actual people with you to help clean up....