Call of Duty: World at War

[King Hadas]

They were doing some pretty cool shit in Africa during WWI, otherwise that war was probably to depressing to make a fun game out of, same thing with Vietnam.

The Nazis were evil as hell and literally trying to take over the world which gives the player a pretty clear goal on how to proceed. WWI Germans weren't exactly cool dudes but other than breaking gentlemanly conducts of war they really weren't any worse than anyone else fighting at the time (most of the horror in WWI was caused by stubbornness and incompetence).

The Vietnam War might be interesting to play from the point of view of a Vietnamese soldier, though that would be pretty disrespectful to are Nam veterans.