Both sides brought it on themselves. In the West, the British and Germans were gentlemen at war, both being warrior nations with long standing war history. And chivilric standings they would treat one another with the most respect, or at least the old fashioned Prussian soldiers would.
On the East both sides hated one another, the Germans saw Slavs as unter-menschen and the Slavs saw the Germans as the worst enemy in the world. In 1941 some Russian and Eastern European towns, and cities waved the invading Germans in because they hated the rule of Stalin. But even since 1939 when the Polish massacred hundreds of German civilians in Bromberg the hatred was present.
Eventually when the Wehrmacht, along with the Waffen-SS passed through the villages and towns the Einzatgruppen came in. Mopping up civilians and taking them away. This had a backlash to the front, which whipped the Russian into returning the favour. Which made the Germans on the front do it back.
Another thing is the Russians were brave, crazy and/or drunk. (
) So the fighting in the air, and on the ground was going to be fierce. Russians were all too willing to ram a plane when out of ammo, anything to stop the Iron Beast which was the Third Reich. On top of that, Russia was where a lot of armoured battles took place. Which were always fierce, with the mass of T-34s against the Panthers and Tigers. Although, the desert had its fair share of armoured conflicts. On equal footing, and hte perfect terrain for armoured tactics. Rommel knew that all too well, unlucky for Guderian he had the Eastern Front from in 1941, and after 'failing' at Tula was relieved of his post. The best general in the war for Gods sake, only stopped by the OKW and OKH. Panzer Army 2 had been fighting for 4 months, non-stop. They needed repair, rest, replacements, fuel but the OKH pushed them further and further. Guderian was up to the task until it was just too much.
Well, I got in the flow there. So there's some reading for you.