In the beginning there was Space War, and it was good. A very long series of "begat"s followed, from Space Invaders to Galxian to Wolfenstein to Doom to Descent, but the arcade shooter's basic DNA remained unchanged despite evolving in complexity and viewpoint. Here is you, there is them, lets trade firepower! The jump from overhead to first person was immensely successful, and there are still literally hundreds of games exploring that space in endless variations. Lose the ground and gravity, however, and all of the sudden the pickings are incredibly slim.