I had a idea from Maplestory which we have Classes. Each Class has it's own boost: Passive and Offensive. Passive will be always on while Offensive is a 'Press Button Move' which could also add the affect of Manna. Offensive will have a duration of 30 seconds. I would think this will increase PvP's uniqueness.
Classes:
-Warrior
Passive: Regain 10 HP every minute
Offensive:For 10 secs, increases attack by 3
-Thief
Passive: Can equip two weapons, second one only being Blue Sword
Offensive: Can go invisible for 5 sec
-Ranger
Passive: Can equip double guns and has more ammo capacity
Offensive: Has 4 soldiers on each side, shooting pistols where ever the player moves (Damage 1)
These are the classes I could think of right now