RecWar, or Recreational Warfare is a really, really, really old game, with Splitscreen and LAN/Internet play against players and bots. It's really quite a blast, with plenty of weapons, game-modes, and all-around fun. It has a map editor. It gets 5 @'s for all-around good times.
What are you waiting for? A screenshot? I beat that tank just below and to the right of my humvee, by the way. All the vehicles handle differently and have minor changes.