I think if we consider 'great' rulers, we consider two factors. One is those rulers who were able to undertake profound social and economic changes in their society as a result of having a clear vision of what would be most beneficial for their people in the long term. Such rulers would be considered 'great' especially if they overcame short term resistance for some clear long term benefits. The second factor of greatness is being able to achieve significant change whilst exercising social compassion. History surely shows that for a ruler to combine these two factors is no simple task! In the twentieth century for example, Ronald Reagan and Margaret Thatcher achieved so much in social and economic reform yet may critics counter that they showed little social compassion, especially with their lack of connection to minority groups or those marginalized by their policies.
The question above actually requires a personal response, so consider what makes not only a ruler great (vision, decisiveness, strength of conviction, ablilty to 'read' the mood of the people), but also those human qualities which make great rulers stand out. In our modern judgement of rulers, the most memorable are those that achieved change because they wanted to raise the status of their people, the standard of living of their people and wanted more social justice in their society.