IMO the Battle of Kursk decided the outcome of WW2 in Europe. Simply put, before Kursk the Germans had the strategic initiative, despite Stalingrad; after Kursk it passed to the Soviet Union who would never give it up. The Battles of Moscow and Stalingrad were big decisive battles, but the key point that distinguishes them from Kursk is that afterwards the Germans still had options. After Kursk they only had one - retreat.
By the time Operation Overlord was launched the war had already been decided for almost a year.
"An Emperor is subject to no-one but God and justice."
Frederick 1, Barbarossa