Clearly I disagree with this sentiment wrt to Saving Private Ryan. It would also overlook movies such as All Quiet on the Western Front (A World War 1 movie following a German Soldier in the trenches). I also disagree that there are more movies about Vietnam than WW2. Maybe more modern ones, but a quick Google search had this chap with a compiled list of 612 World War 2 movies. Many of them older with stars like Clint Eastwood and John Wayne in them. Put Saving Private Ryan up beside some of those 50s and 60s WW2 flicks and see how "typical" it is. You could try watching The Longest Day, but after seeing Saving Private Ryan it just doesn't seem to have the same effect.
Furthermore, I don't recall the Germans being depicted as either cowards or merciless killers either. Certainly not akin to some other World War 2 movies like Bridge over the River Kwai (an excellent movie, but with soldiers running along beaches in their shorts with hot women alongside them in tropical countries, it particularly romantacizes being in the Army and war itself).
None of the german soldiers in Saving Private Ryan acted in an unbelievable way as far as I'm concerned. Sure "steamboat willie" was scared when he was a captured POW, but who wouldn't be. He was interested in saving his own life, as he probably should have been. And if he was let go and found by a german platoon, it's not too much of a stretch to think that he'd fight with them. Yeah, it was a little cheesy that it ended up being him who inevitably shot Miller, but big whoop. It would have been much cheesier if he had recognized him, and then either shot him (or not) afterwards.