As an educator, I used to teach the elements of writing: plot, chactacter, setting, theme, irony, style, and point of view. Recently I've been trying to decide which is most important to me as a reader. It's a useless exercise, since they obviously must blend and blend well to make an appealing book. But preference for a single element must explain the differences we experience as readers. Why do I fail to finish a book that a friend of mine claims is her favorite ever? Why do masses of people buy books with obvious weaknesses in one element or another?
We must have a preference inside us somewhere for a particular strong point that requires the author to deliver on that element even if she fails in some other area. I think mine is plot. I can't say it's always been true, but right now in my life I want something well-constructed and different from the thousands of others out there. Yes, I love a good character, but he'd better not be immersed in a situation no self-respecting character would tolerate.
I'm sure there were times when theme was all important in my reading. Wanting to know what others thought about life was a reason to choose a particular book. I still appreciate thematic excellence but don't generally choose based on that. A well-described setting also adds to enjoyment, but I've seldom chosen a book simply because of that. It's serendipitous that I've learned so much about other places while reading books for other reasons. Irony is greatly appreciated; I love being surprised. Since I've been reading for fifty years and in that time also watched countless movies, I don't count on being surprised very often. There are only so many twists that work in a plot. After that it's just silliness. Style is of course important, but I can adjust to an odd writing style if the story draws me in, and point of view makes little difference to me unless the viewpoint is a character I absolutely hate. A weakness in any of those areas: a character who's a bit flat, a generic setting, a convoluted irony or a run-of-the-mill writing style can be balanced, at least for me, by a plot that works.
So what is the key element in a book? Like the teacher's guide says, "Answers will vary." I find that at this stage in my life, I can forgive a lot if the plot holds my interest and holds together. I don't care if it involves vampires or swashbucklers, takes place in India or Indiana, is told by Will Shakespeare or an idiot. I just want a good story.