I'm working my way through this on the Wii at the moment and it must be said, it's quiet an upsetting game. I think it's the general unpleasantness of it all; it's bad enough running about the Atolls with a flamethrower but when you are marching through Berlin slaughtering every German you come across, it just seems, well, not cricket.
It's definitely the historical context that does it; I have no problems wiping out armies in Advance Wars, Battallian Wars, Space Invaders, Metroid, Jet Force Gemini, Zelda, Doom, Resident Evil or countless other games of killing and destruction. And I didn't mind it so much in Call of Duty 3 - that had more of a Boys Own feel about it.
But this just seems plain wrong. I know WAR IS HELL etc. etc. but while I can watch a film that depicts the violence, horror, futility and inhumanity of it all, it definitely doesn't fit right playing a game that purports to do it.