Without major blunders for the German army, such as the one at Stalingrad, things could have turned out quite different.
The amount of military personnel killed at Stalingrad:
Germans- Almost 400,000. (250,000 of these were surrounded in the kessel, 90,000 taken into captivity and only 5,000 returned to Germany).
Russians- About 700,000
Italians- lost 130,000 men out of their 200,000 man army.
Hungarians- about 120,000
Rumanians- about 200,000 around Stalingrad.
Total- well over 1,500,000 dead.
I don't think that anyone will argue that Stalingrad was not the bloodiest single battle in the history of warfare. It was the beginning of the end for the Third Reich.