I prefer novels/stories with strong character development. I think it's difficult to have an engaging plot without interesting, developed, and believable characters. It is not impossible, though. Ambrose Bierce's "An Occurrence at Owl Creek Bridge" is a good example of a story with an interesting plot and not much character development at all.
Accuracy and voice are the most important elements to me in this category. I would assume accuracy is a given, but I think it is easy to leave your voice/personality out of the piece. Depending on the topic of the novel/story, the factual accounts do not have to be dry and humorless. Put your voice into the piece and do not omit emotion.
Are you looking for information to write a book yourself Loren? If so there are several online resources available including forums where you can ask questions and get advice from published writers.
As for my own personal opinion on fiction I have a bit of a taste for style over substance. An engaging writing style is necessary to a good book. Several famous authors have made a living off of writing a story that anyone could have written but in such an evocative manner that it stands out and makes it a worthwhile read. I hate (exaggerating) Dan Brown but I still made it all the way through four of his novels. He has a certain something about his writing that allows you to tear through a book, hating every second of the terrible plot, without noticing just how engaged you are.
Indeed, I have read few novels (seeming to have "selective dyslexia"), but "The DaVinci Code" had chapters of just the right (short) length - representative of our "Sesame Street" generation. Each chapter presented a corny element of suspense, whose denouement would be found in reading "just" one more. I think Dan Brown cleverly pits mathematics against religion, and vice versa, addictive for the modern proponents of either.
I had considered writing a book of science fiction which projects from real physics. Of course, that's pretty much what my website attempts. I looked into a local writer's group, but it wasn't what I was looking for.
I published some poetry in a university literary magazine. Poetry, with (e.g.) its meter, rhyme, alliteration and metaphor can be much like an equation. I also enjoy meditating on caption contests like that here at PF.