I think Dr. Willis McNelly at the California State University at Fullerton put it best when he said that the true protagonist of an sf story or novel is an idea and not a person. If it is good sf the idea is new, it is stimulating, and, probably most important of all, it sets off a chain-reaction of ramification-ideas in the mind of the reader; it so-to-speak unlocks the reader’s mind so that that mind, like the author’s, begins to create.