If we construct a Cartesian graph with X and Y axes, with X representing the technical merits of the photograph, and Y representing the artistic/social merits of the photograph, then answering the question "What makes a photo great" becomes an exercise in mathematics. We assign a numerical score to both a photo's technical execution as well as the importance of it's artistic/social content. We then plot those values on the appropriate axis of the graph. If a photograph excels in the technical merit - i.e. is well lit, thoughtful composition, in focus, etc etc, but depicts nothing of social/artistic importance, it's plot will fall in the lower right quadrant of the graph. If the subject matter is of significant artistic/social importance, but poorly executed from a technical standpoint, its plot will fall in the upper left quadrant of the graph. In both cases, the photo has failed to achieve an measure of "greatness". Only a photo whose plot falls in the upper right quadrant - one that is of a worthy artistic/social subject but also technically well executed - will be considered a "great" photograph.
Of course, all that is a load of s**t - nothing more than a tongue and cheek nod to same simplistic analysis ridiculed by Robin Williams' character as the literature teach in "Dead Poets' Society". But I just couldn't help myself. When I read the question, that scene was the first thing to pop in to my head