I’ve commented on this before, but it’s worth repeating: I hate meta content in books. Chapters and chapters where every paragraph mentions things to come later or details that will be covered in the course of this book or stuff that will be discussed in part II. Write the content of the book. Then complete the book. Do not provide extensive introductions, commentary on things to come, or try to sell the reader on the book once they’re already reading it. I have a similar aversion to frequent summarizations (read: one per chapter when chapters are 1-2 pages), bullet lists of key points, and other PowerPoint-ready isomorphisms.
I think much of what I read could be made 20-30% more effective just by culling this meta content. The books would also be smaller and cheaper. I guess that would suck for publishers. There is an art to being succinct, and saying what you want to say once. If the point is important, you need not beat the reader over the head with it. Either they will pick up on that because it was well written and they are not stupid, or they will not.