The Battle of Stalingrad became a turning point in World War II primarily because the German army exhausted their supplies and suffered a devastating defeat. The battle, which lasted from August 1942 to February 1943, marked the first significant defeat of the German army, which had previously been on the offensive.
As German forces became encircled by the Soviet Red Army and faced harsh winter conditions, they ran out of supplies and were unable to sustain their positions. The loss at Stalingrad not only resulted in the destruction of a significant portion of the German Sixth Army but also boosted Soviet morale and marked the beginning of a series of successful Soviet offensives that would eventually push German forces back towards Berlin.
While it may have had personal significance for Stalin, the critical factors that made Stalingrad a turning point were the strategic defeat of German forces and the shift in momentum in favor of the Soviet Union. The other options you mentioned, such as the idea that it marked the beginning of Germany’s victory or that the German army gained hundreds of soldiers, are inaccurate in the context of the battle's outcome.