What is extremely rare is a Mafia FPS. The only one I could find (which is pretty decent) is Mod Enforcer/Chicago Enforcer. Both're the same.
I'd like a Vietnam War pack. Dang it, if only I could model and animate hands/arms, weapons, water, jungles, enemies, etc. other Vietnam stuff.
There are at least a gazillion WW2 games out there. A scifi game, Halo, anyone? Urban games? Battlefield 2, Rainbow Six 3, Ghost Recon, etc.
If there was a script to implement Splinter Cell-like stuff, like destroyable lights, dark good, light bad, etc.
Another rare genre is Civil War. Only that Civil War game on the XBOX360 is the ONLY Civil War FPS out there.
Just play some games, look at 'em, and get some ideas.
Automatic: Biological Warfare
Comin' soon, maybe in Jan./Feb. 2007!