Your comment about modern MoH/CoD spin-offs doesn't make sense - of course I was talking about first parts of the series set in WW2. Am I that hard to follow?
I recall using a bipod on LMG in one of CoD (WW2) games. Sharpshooting with a bolt-action rifle was the biggest fun for me. It's challenging to aim well in a firefight, as reloading takes time. So it wouldn't be a problem to repeat this in WW1 setting.
My comment about American Civil War was aimed to counter "it's not as cool as WW2" argument (used against WW1), I wasn't thinking about FPS games in ACW. By the way: the only one I found unfortunately mixes in some future time travel themes:
http://www.mobygames.com/game/darkest-of-days/
I still don't know why are we still talking about major battles in all those wars - we are not discussing wargames, after all. Aren't we often sent on a special missions in those WW2 FPS games? In small teams or even alone? Scouting out, infiltrating?