What struck me was a bit that probably piques the interest of most writers who read the book: Mr. Rochester's description of what it's like to be a character in a novel.
Mr. Rochester and the others do not lead a linear existence, but live the story in an infinite loop. Their lives aren't linear even within the loop: they experience their part in the whole story simultaneously all the time, but each character can choose where to locate the majority of her/his consciousness at any given time. Naturally, Mr. Rochester spends most of his time hanging out at the parts of the book when he's happy with Jane.
As far as free will, the characters seem able to do whatever they want as long as it doesn't contradict what's written. They have to do and say what it's written that they do and say, but they can do anything else when they're offstage, especially when the book's narration is limited (e.g. when the narrator of a first-person story can't see them). This becomes especially interesting when combined with the fact that the whole simultaneous-experience-infinite-loop thing means that they know exactly what's going to happen all the time. They have to make the same mistakes every time, no matter how they seethe about it inside. They're much like actors.
My reaction to this was almost exactly the same as my nine-year-old self's reaction to seeing Toy Story. "Hey, that's cool!" segued immediately into, "Hey, I wonder what mine would be like if they were alive like that!"
Naturally, one doesn't write books picturing the characters this way, unless maybe one is writing highly experimental meta-type fiction. Even in The Eyre Affair, which kind of IS exactly that, the characters aren't written this way. But if the characters in your novel did live, and lived like this, what would it do to their psyches? If they knew everything that was coming, which parts would they relish, and which would they dread? How would their feelings during different scenes change if they knew everything that was going to happen? (I see some villains feeling very bitter as they deliver their triumphant speeches, and a lot of characters mentally rolling their eyes as they muddle through romantic misunderstandings that they actually understand completely.) What might they do differently during their off-page time? Perhaps most interestingly, where in the book would different characters focus their consciousness?
A lot of questions about characters' lives aren't answered in The Eyre Affair. What's it like to have backstory that you never technically experienced, because the whole of your existence takes place over the course of the book? When you're offstage, can you do all kinds of death-defying things because you know you can't die given that you appear later in the novel, or are you simply blocked by the fourth wall from trying such things? When the POV is close enough to include thoughts and feelings of one or more characters, are those characters constrained mentally and emotionally as well as physically to the plot, and how does that work? I may actually read the sequels just to see whether more of this comes out.