I did reduce the damage the archers do, and they're slightly more vulnerable. There's almost no deviation in accuracy on the short range now (which was stupid I must admit), there are slightly more enemies after you finished the game to make it a little harder. And the health now comes at three different costs depending on how much health you have. I'll keep looking at the comments to see if more things pop up.
A little note from the author here :) This game is not in any way meant as a pro-Nazi game. The fact that no matter what you do, you'll lose in the end and the sad music when you die is in fact only there to signify how pointless war is in general. Lot's of lives are lost for unnecessary causes. Although I must stress that the Allies invasion on D-Day was not serving an unnecessary cause, as it ultimately ensured the freedom of all of Europe.
Little symbolic things such as Nazi occupied France being portrayed in a red colour, and the Allies in blue are there to symbolise the fact that the German army here is the 'bad side'. This game was not made to force some kind of idealogy upon the player.
Thanks for all the comments so far!