Walk, Run, or Jog?

Recently, I was reading an extremely long (quarter-of-a-million-words plus) book that shall remain nameless to avoid embarrassing the author. It held my interest enough to get me through to the end, but it left me curiously unsatisfied, with very little memory of the plot (which is quite unusual for me), and no impulse whatever to reread it. I mentioned it to one of my friends, along with the joking comment that I should really sit down in my copious free time and analyze the book to see...