I personally think Stalingrad was a disaster completely due to the top command.  Paulus was directly pressured by "The Great Leader" to march in and take the city.  Hitler didn't want a long siege even if it resulted in eventual victory.  He thought the Wehrmacht should be able to waltz in and destroy the Russians.  However, Stalingrad is a long and narrow city running along a river.  This gave them at least a seven or eight mile front, fighting through dense urban areas.  This was much more easily defended than attacked.  If the Germans had instead crossed the Volga and completely encircled the city, their soldiers wouldn't have had to enter the urban areas until they were demolished by artillery and bombers along with everyone in those areas and the Russians would be completely unable to reinforce or resupply Stalingrad.  It was senseless to demolish an area and turn it into a cratered quagmire only to have it reoccupied with fresh troops and then have to fight through rubble and craters.  Assuming Paulus could have had free hand in the campaign (without Hitler ordering him to march straight into the city and not give up an inch of ground at any cost) and had the combat sense to effectively plan and execute a logical attack, Stalingrad could have been quickly cut off and captured.  This would have pushed the main battle away from urban areas, into the open country where the German's had proven their ability to defeat extremely unfavorable odds against the Russian armies.
Just my two cents.  (And I do admit that I am merely an amateur of history and it very easy to make conclusions long after a battle has been fought.)