Is the Bible a work of fantasy too?
Nah, aside from the 'Preach and Conquer' RTS I had in mind, I've always wanted to see a game based on the Mad Max movies. Nothing like Fallout though, this is more of a game like the Falcon flight sims. That is to say, enough landmass to fill all of Australia and roads that stretch on for weeks in any direction (time compression a la Falcon would be optional).
And there would be car to car combat as seen in Interstate 76. Stealing fuel, raiding/protecting villages. An extensive RPG system that includes advanced engine mechanics aside from the usual stats and skills. Things like welding together new parts that have broken down, creating new parts, fuel consumption and modifying other aesthetics about your car that come with advantages of their own.
Oh, and a really sharp metal boomerang.