What makes a great short story?

I think I find the short story the most difficult form to write because I am a lover of plot and narrative. A storyteller. The great short story is essentially an epiphany, a meditation. Nothing dramatic need happen. The change, or transformation in the character or characters is internal, usually subtle. But we are made to care about them, be curious about them, as we are enticed into a story that gives us a glimpse, or more, of an entire emotional landscape. I am thinking, in particular, of short stories by Anton Chekhov where nothing much happens overtly, but we sense a shift in feeling or perspective. 
There are, of course, well-known writers who rely almost solely on plot, with a twist, or a sting in the tail. I’m thinking of O Henry, Roald Dahl, and Saki. 
One of the greatest short story writers, Guy de Maupassant, combines, plot, character insight and emotion. His best-known creation, ‘Boule de Suif’, is the first short story I remember reading as a young teenager. It has remained with me ever since. As has the classic O Henry story, ‘The Gift of the Magi’. And, of course, ‘The Dead’ by James Joyce - characters we care about, contemporary events which interest us, widening into a meditation on life, love and death. Sheer genius.