I will say there are 4 keys to being a great RB. In no order to relevance: 1. Power 2. Speed 3. Vision 4. Balance
You can look back at all the greatest RB's of all time and not many had all 4 but most had enough of all of these characteristics to make him great. One of the greatest assets a Barry Sanders, Emmitt Smith and Walter Peyton possesed was a supreme vision on the field. They could see the play before it happened and knew exactly when the holes would open or close down. Now of course they all possessed great athletic ability but it was their vision on the field that made them legends.
Vision, vision, and Oh some more vision. I think we have one on the team now that has good vision but once he gets into the open space the turf monster trips him so for him balance.