How about this: Ranking system. You can chose differant vehicles at the begining depending on Rank. Kills, rounds won, will add to your score and help you get a rank up. Maybe for differant maps you can run over bonuses. Like in the movie, swords would give your car ammo, and shields could repair your car and add armor plating.
And to try and stick to some realism, lets say its post-WWII, and the Axis and Allied troops are slowly destroying all the cars left over from the war.
|