PvP essentials.
Balance: A skilled person should be able to kill an unskilled person who is a "higher" level. The "widgets" and stat points should not determine the outcome. If a person 2 levels higher cannot be killed ever, then that part of balance is gone.
Balance Class: There should not be an uber win every time class.
Balance Gear: There should not be a single uber weapon which guarantees victory.
Risk: You should lose stuff and/stats upon death. Without risk/danger there is no underlying drive to fight like real person on a battlefield.
Reward: There should be a true reward for overcoming others. "kill points" are gay and phantom. you should be able to take a piece of that person in game (remember taking heads in UO?).
Good pvp Games (my opinion): Tradewars, Jumpgate, Dread days in UO, Shadowbane.