If you have got bored with Thompsons and MP-40s and fancy going all old-school maybe this title announced recently 'To End All Wars' oot next summer, will be more your cup of tea. 'Set in the war-torn trenches of World War I Europe, “To End All Wars” will deliver unrivalled atmosphere and realism, bringing the mud strewn horror of this most desperate of conflicts to the PlayStation®3 and Xbox 360TM formats using Epic’s Unreal® Engine 3 technology.' Ghostlight site
There's also The Trenches, a Half-Life modification if that's your bag. Looks interesting. We've now had American Civil War - what's next The Alamo? If you don't know what an FPS is then look here.