If you are doing good in photography, it is simply good photography. But if it makes a difference, it's great photography.

Good photography means a photograph which be able to communicate with the viewers  and be  able to tells a story is called good photography... 

Great photography means a photograph which reflects the actual quality and creative efforts is called great photography

If your Photography creates impact and is unforgettable & appreciated and used by most of the peoples then it's great photography like Dabboo Ratnani Calendar shoot. But when you are not able to create an impact on someone then it simply good photography.