Multiplayer via WiFi, evdo, or Bluetooth. A good first person feel with the ability to easily walk and aim using the native controls. Graphics that are at the native resolution for the phone. Statistics and award system. Chat and or voip. Integrates with wired and Bluetooth accessories. Player modifyable content. Ability to run your own server. 3d graphics. Perhaps mobile ports of popular pc games. Customizable player avatars. Squads. Squad commands and general commands and taunts for quick communications.
i forgot to add:
The use of the accelerometer, maybe gps, and magnetometer to look around the environment and aim. Walk forward, backward, fire, and strafe could be on a button.
Be even nicer if you could have a "live" game mode and chase other Android users with augmented reality and find them via GPS and use your phones camera to fire at them. They would then take damage and would have to wait a few minutes to respawn. You could then have stats, or locate items in augmented reality.