What I personally think would work far better than a WWI game (a conflict which, most people seem to agree, doesn't seem to translate well to the third or first person shooter, or RTS genres), would be a game set during the Russian Revolution and Civil War (1917-1923, a similar period).
While it might be necessary to have our hypothetical hero be betrayed by his Communist superiors, due to the Soviet Unions errr... image in the western world -there is such a wealth of material, that if you were set on doing a game in this period, I think the Russian Revolution would be the logical choice.
Just off the top of my head, our game could begin with a bit of backstory on our character- maybe he could have been one of Rasputin's assassins? And have gone on to nurture revolt in the capitol? Which would then transition nicely into the butchery that the Tsar unleashed on the protestors in Petrograd, in the final days of his rule- heck, you could even make it a tutorial if you liked- fighting back soldiers and mounted Cossacks with big fuzzy hats.
From there, maybe to the Kornilov revolt- give us a little cutscene about being imprisoned when the new government came to power for the deaths of those men, and then let us loose again from the prison, along with all the rest, with a rifle and a big old pistol to prevent the General and his men from succeeding in their coup...
And on and on- to Petrograd in October to fight through the streets and capture key buildings- the armory, the communications buildings, ect- and finally an assault on and through the Winter palace (I know, this part was nearly bloodless, but hey, artistic license is available when making a game...).
Then next, across the Russian tundra by train in winter, to capture the Ukraine and fight against the counter-revolutionary White army- and so on and so forth, maybe to our dramatic betrayal, and turnaround.
Anyway, what I'm trying to get at is that not only is there lots of very dramatic material, and some very varied locations and scenery, but there is no trench warfare! We've got house to house, through cities, palaces, and across the Russian plains (into the mountains even, if you like)- but all of this would mesh much better with the style of shooter people have grown used to: fast paced, lots of movement, and some cover, if our hypothetical dev were to take it in that direction, than trench warfare would.
(And hey, some of those locations would be pretty cool- I'd rather poke my rifle aroud a banister in the winter palace and have someone try to blow my head off than fight through muddy, mortar-shelled-plain + hill #23.)
