I like reading author's notes, acknowledgments, and introductions because they're sort of the book equivalent of liner notes. Things that are good on their own take on a more nuanced flavor for me when there's context. Even small details that ring off of one another unintentionally have a zing to them.

I'm willing to bet that this characteristic is a geek trait, or possibly a fannish trait, because it seems to be the root of that impulse when I make my mother watch Doctor Who to try and get her to pay closer attention to the small details because they pay off later. I also really love in-jokes, coincidences, and synchronicity. Ah, the pattern-loving brain.

I think I might be curious to read a little about your expectations about the series when you set out versus how it ultimately played out and your view as an author finishing them up. I'm guessing you can't put a whole essay in there, but I'm also a sucker for seeing things play out on the way to a great payoff.