Maybe I have watched too many WW II movies, but here's my take on why Germany "lost" WW II:
1. Germany's invasion of Russia in September was a bad move because they ran into the Russian winter. Had they invaded in the Russian spring they would have had a whole summer for action against Moscow and maybe Stalingrad.
2. Germany ended up fighting a two or maybe it can be called a three front war: Britain and western most of Europe, Russia and southern Europe (Italy/Mediterranean/North Africa). If they had just conquered Russia first, then the West may have had trouble beating them what with the resources they may have gained from Russia including oil, steel works, technical know how, manufacturing capacity, and man power.
3. At the battle of Stalingrad Hitler split his forces - one to take the city and one to go for the southern oil wells. The Germans should have gone for one or the other but not for both. Of course, Goering promised he could supply the German army there, but that didn't happen. Of course, by item 1 above, a three or four month head start might have been successful considering the winter situation.
4. The Germans were in love with technology and size. The tanks developed and used in the Battle of the Bulge were enormous and inappropriate for the forested/hilly/river containing terrain on the way to Holland. These tanks couldn't cross bridges because they were either too heavy or too wide and they used a lot of fuel. The Sherman and successor tanks weren't the technological marvels of the German tanks, (and those of the Russians) but they were reasonably reliable and repairable by their crews, large in numbers, maneuverable and more fuel efficient. Other choices by the Allies about what to manufacture in huge numbers and appropriate quality were also important.
4. And of course the incredible cryptanalysis capability of Bletcley Park that resulted in the defeat of the U Boats and kept the supply chain running to Britain and Russia from the U. S. as well as the defeat of the Germans at Kursk the the Russian advance west.
I'm sure others can add additional "mistakes" made by the Hitler-German war machine that resulted in Germany's defeat including the nature of the German army's culture of following orders, even if they came from a mad man.