I just realized that I haven’t actually answered the question for this thread, so here it goes:
A good book to me is one that allows me to be engaged with my imagination, which also requires a certain level of depth of content and display of wit. Looking back at my TOPHAT application and the five favorite books of mine that I put on there, the common threads that I can see among them are their depth and a demonstration of composition that the author understood the target audience and book purpose.
Plot and characters aren’t necessarily important to me, as some of my favorite books have neither, but accessibility to my frame of reference is paramount to me being able to engage with a book. This includes the vernacular that a book uses and the presentation of its information.
Since some people won’t see the picture Franklin posted in the comment above, I’ll transcribe it here:
There are three books in the picture. The three books stand side by side. They are entitled “The Two Towers”, “The Fellowship of the Ring”, and “The Return of the King”. All three are written by J.R.R. Tolkien.