Agreed with the above post. Hitler made a grave mistake by invading the Soviet Union, which outnumbered him three to one in population, and had massive distances and areas to contend with. It's unconquerable without nuclear weapons, much as the US is. By staging the attack, it guaranteed that he would lose the war.
It was also one of the most destructive, brutal and bloody wars in human history. 20 million Soviets died and 3 million Germans were killed. Entire cities and states were laid waste. There were massive refugee populations, 1.5 million Jews were murdered and thousands of war crimes were committed by both sides in the war. Stalin refused to trade for his POWs (including one of his own sons), and refused to give back any German POWs. Most of them died in Soviet labor camps.
Indeed, the miscalculation in believing that Hitler could overrun the Soviet Union is where the greatest result from the campaign exists. I think that Hitler's desire to go after Russia, similar to Napoleon, bogged him down so much that fighting on both fronts became nearly impossible. Another reason why it was significant was that the conflict displayed two similar leaders, once aligned with one another, now actively against one another. Stalin and Hitler were two leaders cut from the same cloth and their conflict in the Eastern theatre was so intense because it represented a similar magnitude of leadership seeking to overwhelm the other. Both of these dictators' attacking one another, allowed the other two of the "the big three" to attack Hitler from the West and helped to ensure an Allied victory in Europe.
The German invasion of the USSR is seen, in hindsight, as one of Hitler's biggest mistakes. When you see books or shows about mistakes that lost World War II, this one is always included.
When Hitler invaded the Soviet Union, he thought it would be an easy win. Instead, the German army ended up getting bogged down in the Russian winter and was never actually able to conquer Russia.
Germany kept fighting until the very end, but this invasion (when they had a peace pact with the USSR) ended up losing Germany huge amounts of equipment and huge numbers of soldiers.