Another complaint that keeps a story from getting 5-stars is too many characters. I would amend that by saying too many extraneous characters. Every person should be tied into the plot in some way and stand out as an individual. If they don’t, ditch him or her. If you really like the person, you can always use him or her for another story.
This is not to say that a meaty plot shouldn’t have a vast array of characters. However, the number should be proportionate to the complexity of the plot and length of the novel. Populating the story with a bunch of people with no story function only keeps the reader wondering what they’re doing there in the first place. For example, if your protagonist’s job is one of the settings, you don’t have to give everyone a name unless the person relates to the story. In fact, if their place of work doesn’t relate directly to the story, why is it included, anyway? The movie “Nine to Five” certainly was an exception, as well as the TV show, “The Office.” But if it’s not directly related to the plot, minimize it or leave it out completely.
If you do have a long cast of characters and you can justify their existence, then include a dramatis personae in the beginning to help your readers keep them straight as far as where they fit into the story and relationship to one another. A confused reader is inclined to become a lost fan.