Ok, after finishing my last game, I got a rating of Pathetics. I know I played on Chieftain, but I was light-years ahead of everyone in tech, number of cities, military power, and culture. How do they determine your rating at the end anyway?
After you finish the game and the score is calculated using such numbers as the number of happy citizens, techs, wonders, etc., the score is multiplied by a constant, which is determined by your level of difficulty. Well, chieftan really makes your score lower.