An interesting line of thinking, but fraught with undefinables; e.g. "great". How does one even define the word "great" as it applies to photographs? Beautiful? Visually compelling? Emotionally evocative? Thought-provoking? Artistic? Unique? Universal? Timeless?
Great to whom? The artist? The general public? Art snobs? Gallery owners? Ad "men"? Furniture dealerships?
Great technically? Visually? Compositionally? In IQ?
These are words/concepts that float around in my wee pea-sized brain when considering photographs posted here and elsewhere, in fact any time I see a photograph. But, the bottom line is, a natural landscape (sans "the hand of man") that is intensely emotionally evocative, timeless and visually compelling, technically perfect to me, means very little to others here and elsewhere. And street scenes of people who are engaged in nothing more than anthropocentric self-absorption (the way I see a great many public human interactions) are full of meaning and nuance to others here, hence my complete ignorance when it comes to street candids.
When photographing, all we can do is work to please ourselves (unless a commercial client is footing the bill!). If someone else is moved by your work - great! If not, you have something for your walls or screens that will, at least, give you some satisfaction. If your work is unique, compelling and thought-provoking AND is in front of the right eyes at the right time AND you have an interesting backstory, your work might just be considered "art"!