Please remember, the aim of the documentary is to emphasize what is often misrepresented therefore the perspective is, I think, both expected and acceptable.
The Soviet Union's part in WWII is hardly controversial, atrocities are also shown so I can bear with some effects and music when the Russian people do some extraordinary things, as with other nations in the series.
Allies facing 10 German divisions on the Western Front, Russians facing 200 German divisions on the Eastern Front, is an undeniable fact in the historical record.