What separates a good doctor from a great one?

Combination of. . . Natural intelligence, superb training, experience and ongoing learning, caring compassionate attitude, and humility to know they're not always right. Kindness towards our fellow beings, regardless of age, race, status, or wealth. Inquisitive and understanding. Giving and charitable. You'll know when you meet one!
Good question. I doubt that you will get a consensus on this, but i think great doctors not only have knowledge, experience, good judgment and competence, but also have compassion, honesty, listen carefully and have humility.