This is a little off-topic, but if you want to play a really good game about The Great War, then play The Last Express!
It's set a few days before war breaks out, and a lot of the story is foreshadowed by the war that you know will happen. A lot of the characters are representative of the forces in the war, as well, and it ends in a similar tone to the one Neon Git was suggesting. (See the game's making of video for more information -- http://www.youtube.com/watch?v=ddWb4LX69sE
). It's not a first person shooter, but it is a first person adventure!