What makes it great is (a) that the filmmaker tried only to use source material, including audio narration, created during WWII, and (b) that the film sources were shot in color (rare for the time).
There's a YouTube channel called "CHRONOS-MEDIA History" that has a lot of archival footage from that era. A couple ones I found interesting were a clip with American and German officers casually working together to coordinate a German surrender/withdrawal at the end of the war, and a German propaganda piece from before the war (?) where the skyline of the village they're in matches 1:1 with one of my vacation photos.
"Stalingrad" is a horrifying documentary about the battle. It's recounted by the German and Soviet soldiers who took part. The takeaway was that given the right incentives human mass depravity is bottomless.
What makes it great is (a) that the filmmaker tried only to use source material, including audio narration, created during WWII, and (b) that the film sources were shot in color (rare for the time).