Sorry I think a Wehrmacht focused FPS wouldn't realistically work for so many reasons, practical and theoretical ones.
First, in practice FPS are usually big budget games with large publishers behind them which need to make a lot of money, and let's face it, a game like this will just be much less popular with the general gaming audience than a game where you play the good guys.
(Although things are obviously never totally black and white, overall I think it's a fair generalisation to make that in WWII the Germans were the "evil" side and the Allies were the good ones. As for Russia, well in CoD you kind of see how that can work: They are displayed in such a fashion that they are clearly not the good guys, but at least you are fighting someone at least as evil, plus you're fighting in a defensive war at that point.)
Second, even in principle I can't see such a game working very well. I think one motivation of playing a (single player) FPS is to have something to root for. Playing the evil side can work, but more in a fictional over-the-top setting (Star Wars for instance).
As for FPS as a platform for artsy, reflective, subtle games... really? A FPS is about killing things, after all. Not to say all FPS have to be outright stupid (think Deus Ex), but how would such a FPS about the Wehrmacht even look like? Missions where you kill hundreds of people, then cut scenes that show you the cruelty of war / the nazis? Missions where you try *not* to kill people?
But yeah, if you're able to actually integrate the part about the "guilt" of the average wehrmacht soldier, about how much they knew, about how they were in conflict and whatnot, MAYBE, just maybe you might be able to create a "tasteful" and good game, maybe something that even educates people.
In a FPS game? Any game like this, I'm pretty sure, wouldn't be fun to play at all.
Really, the only way I can see a game that involves fighting for the Wehrmacht happening is one where you end up not fighting for the Wehrmacht after all. E.g. one where you start fighting for them, but then desert/ join some resistance group or whatever, or an alternate history one where you end up assassinating Hitler/ fighting the Nazi machinery from within...
That, actually, could be a pretty cool game, even educative (slowly seeing through the propaganda and stuff).
Edit: Jnecros, like I said I think it's a pretty fair judgement to make that overall, the Germans *were* the evil side. Facism, holocaust, overthrowing democracy and murdering its proponents and intellectuals, and an expansionist aggressive all-out-war... no, I don't think you can attribute something similar to say the British, French or Americans (in that period of time). That doesn't mean you cannot and shouldn't learn lessons about things being not totally black and white, about the other factions doing evil things as well, or learn about not all or even most Germans being simply inherently "evil", but still.
(I'm German myself btw)