As noted, Stalingrad cost Hitler the war. Ironically, at the height of the German advance into the Soviet Union, Axis armies were only about 12 miles from Moscow. Had Hitler pushed his advantage and taken the capitol, the Soviet Union might well have capitulated!
The fact that he did not, and placed his bets on Stalingrad shows his degree of megalomania -- Hitler chose to humiliate the leader of the Soviet Union by controlling his namesake city, rather than controlling the more strategic capitol city.
What's in a name? How history might have changed if Stalingrad had remained as Tsaritsyn!
Hitler's desire to control Russia (by breaking the treaty with them) proved to be his undoing. The large number of men he committed to the Eastern Front left his other armies in Europe and North Africa undermanned; and the eventual losses in Stalingrad--more than a million men--sealed his doom for controlling the entire continent.
Hitler's defeat at Stalingrad marked a decisive turning point in the war. Enormous numbers of men were lost and any chances or further forward movement were lost. The Soviet victory inspired not only the Soviets but the other Allies as well. By the same token, the defeat at Stalingrad was tremendously dispiriting to the German forces and population.
I believe the most important result of Midway was that the Japanese navy lost 4 aircraft carriers, which in the war in the Pacific was devastating, since carriers were the backbone of both fleets and essential to offensive operations.
At Stalingrad, not only was the German invasion turned back, but they lost an entire army, over a million men. It was a staggering defeat that changed the momentum of the war.
Coral Sea was the first time the US didn't lose to the Japanese and Midway was a huge Japanese defeat. At Midway, they lost carriers and pilots, neither of which could easily be replaced. From then on, the Japanese were never able to attack again, they were just being pushed back. The same goes for Stalingrad where the Germans lost a huge number of men and a lot of materiel. From then on they were getting pushed back too.