I'm in the process of editing a book of stories, to be published in the New Year. They vary a lot in length and subject; there's good neighbours, murder, art, a strange voice, sadness, joy, cute children with unusual abilities, older people and much more.
During the writing, I read a lots by other people. Some impressed me, some didn't, and quite a few I didn't understand at all. So what are the ingredients of a good short story? What does it need to give the reader? I've come to the conclusion that a good short story, first and foremost, should be a story. Obvious, for sure, but it's a basic that's not always there. It needs a beginning, a middle and an end, just like a novel. Of course, there is no end to a novel, there's always more beyond, but it's the end of the story within the bigger story.
A short story shouldn't be a tease, there should be a resolution at the end, or a sting in the tail. It's good if the reader feels satisfied, but also wants more. That leaves space for the imagination without frustration. My personal test is to ask, "Could this be extended into a novel or be part of a bigger story?" If yes, then it probably passes as a decent enough story. Also, it should flow well and be entertaining, but have depths that readers can to explore if they wish. The short story leaves plenty of room for the reader to fill in the background and characters. Description needs to be enough to invoke the pictures, but not so much that it distracts from the story. So there we go. Simple! - but I didn't say it was easy!