I had this idea for an FPS. There is a war, another more advanced civilization invades your nation, with cyberpunk technology, and you set up a valiant defense with your inferior steampunk technology. In the end your civilization is destroyed.
You would be able to freeroam ala borderlands or fallout 3 in an industrial steampunk city.
If that game were to be made, and were to have a multiplayer mode (humans vs clockwork men), and a trailer was to be released, I would literally jizz rainbows.
Also, a proper sequel to F.E.A.R.