In the preface to Artificial Intelligence and Literary Creativity: Inside the Mind of BRUTUS, a Story-Telling Machine, Selmer Bringsjord and David Ferrucci argue that a good story, whether generated by man or machine, needs "wide variability."
There are many dimensions over which a story can vary. Plot is only one of them. Characters, settings, literary themes, writing style, imagery, etc.–these are other dimensions, and there are many more. Generally speaking, belleteristic fiction has very wide variability across these dimensions. Mark Helprin’s latest novel is likely to have a rather unpredictable plot traversed by rather unpredictable characters in rather unpredictable settings tossed by unpredictable mixtures of love, revenge, jealousy, betrayal, and so on, as reported in prose with a cadence and clarity rarely seen. One of the chief effects of it all is to conjure unforgettable images in the reader’s mind. (One of us is haunted weekly by the image of the lost gold in Helprin’s Memoir from Antproof Case.) At the other end of the spectrum fall formulaic fiction and film; here the variability is narrow. Some romance novels, for example, fail to offer wide variability of plot and characterization: It’s the same character types time and time again, dancing hot and heavy to the same choreography. If Brutus^n, some refined descendant of Brutus^1, is soon to find employment at the expense of a human writer, in all likelihood it will be as an author of formulaic romance and mystery.)
The preface is available as a pdf file on Bringjord’s web site.