"What is important for a great photograph"
That is a question that has an answer that is both an opinion and facts. We all, as photographers, can sit down and list what it takes to make a great photograph and a lot of the answers might be the same across the board. For a great photo, that then becomes an opinion and with as many photographer that are in the world, you can get that amount of answers and they would all be correct.
There is a photo that was taken by Robert Capa on the morning of June 6th, 1944, that by all accounts would be a bad photo. It is out of focus due to camera shake, Shutter was also slow, the grain is really bad, it looks like the wrong aperture was set. On the other hand, when you know what was going on when the photo was taken (which, I am sure most people can guess by the date),you can see why it is one of the greatest photos taken that day.
D-Day | 100 Photographs | The Most Influential Images of All Time
There are many things that can make a great photo. At the same time, there are many different opinions of what a great photo is.