The Germans were overrated in the sense of people thinking they were invulnerable; Germany had an early advantage of being an aggressor who had prepared for war. Their tactic of blitzkriek were
well-defined and indoctrininated. The German forces were very flexible, and less rigid in their tactical approach to battlefield situations. They were highly mobile, and their tanks were well equipped with telecommunications. They had the best tanks, aircraft and infantry equipment.
The Germans were not unvulnerable. They relied on horses. The German military had weak resources of fuel/oil, and was forced to adopt creative solutions to these problems. The German Army was extremely vulnerable to morale problems due to its policy of ethnic cleansing/genocide. The German Army committed acts of mass murder ie. it exterminated 1/4 of the entire 4million population of Moldova. The German Army rolled into countries bringing with it mass murders of civilian populations and the seeds of guerilla warfare fought desperatly against such onslaughts. Also, the Germans bombed extensively civilian populations as well as military targets. The USA didn't lose
and strugglr against the Germans as much as other countries due to its late entry in the war and its relatively low numbers of contact with German forces. For example Russia lost more soldiers in the singular Battle of Stalingrad than the USA lost in soldiers in both the European and Pacific theatres of the War combined. The Russians had 5 such heroic cities desginated as such due to their harsh battlegrounds in their stance against Germany's aggression.
The Germans swept through Russia and initially were very successful ie. they were racking up statistics almost exactle the same as those in the invasion of France. Army after Army of Russian soldiers were being enveloped by the rapid German blitzkrieg. The German airforce was detroying the Russian airforce before it could get off the ground and interceptthe German drive forward. Millions of Russians were taken prisoners. Civilian populations were subject to cri,es of rape and mass murder. Russian children died from being used for blood tranfusions to wounded German soldiers.
Refugees from the holocaust in Eastern Europe had fled East into Russia. The Russians laid over 900miles of defensive workd before the gates of Moscow. Today there is a statue of Marshall Zukov
with one palm lifted up...and the quotation below readds 'They shall not Pass...'
Germany was perplexed ie. it had captured and killed millions and millions of Russians, and wiped out entire armies. Yet as winter came, and as their tanks and other equipment broke down and became vulnerable requiring massive overhauls and maintenance, there gradually emerfed some troubling signs. Despite, the heavy body count that German experts interpreted as Russian defeat,
and despite the terror the German army had inflicted, there were active partsons in their rear disrupting the German supply line, and there were no Russian war factories in reach of German bombers...so there was a sense of forboding because the Germans realized geographically they were deep in a country that had vast lands and factories and population far to the east out of range that was now preparing a vast counteroffensive while partison forces disrupted the German rear.
The German stats were wrong and the Russian Army launched its own blitzkrieg, wiped out the entire German Army at Stalingrad and relentlessly
tore the German army to pieces sending it reeling back into Germany. This fighting was very bloody.
Germany and fascist Polish troops at one point put 70,000 Russian prisoners on locked railroad cars
and abandoned them to die of exposure.
The German Army adopted an official policy of total ruthlessness ie. it gave no quarter, especially if you were Eastern European or Russian. British and American prisoners were treated relatively well by comparison. Germany guillotined over 100,000 German dissidents during the WW2 era.
Britain was subjected to massive bombing and V2 Rocket campaigns that hit mostly civilian targets, the idea was that such terror weapons would weaken British morale but it tended to have the opposite effect. In Russia too, the people rallied around Stalin instead of abandoning him mainly because he became perxeived as a patriarchal icon of Russia itself embattled against the German onslaught. I believe American heroism was most personified in the air war against Germany, and while Germany was initially successful, the mighty long range USA bombers were superior and could not be stopped. Such US aircraft as the P51 Mustang could not be matched by the German airforce. I would say that the allied airwar over France and Germany was in a sense the Wests's Stalingrad.
Germany initially had a technological advantage, but it lost that advantage by 1943.