Stalingrad is one of my 'favorite' (is that the right word) battles of WWII, it still amazes me that the russians managed to hold on and beat the germans, I recall reading that the t34's were rolling out of th efactory not painted and going straight to the battle so desperate was the russian predicament
The determination of the Russians was the winner in this battle, at this stage the battle got to a stalemate, Hitler lost the plot, the Germans couldnt replace the dead or injured soldiers with the same experiance. From here the Russians just got more confident after they realised the Germans were at a stand still.
See the "Operation Uranus" Section. The Russians knew that the Wehrmacht was being stretched thin in the Stalingrad area. The 6th Army was taking losses at an alarming rate once the fighting reached the city itself. They had no option but to strip the flanks to replace the losses. This then left weaker allies (Hungary,Romania & Italy) to fill the gaps and of course these were not so well equipped as the German Divisions. The Romanians in particular were relatively ill equipped for the task they had to perform.