Like Eric Klingenberg, by coincidence, I've just started to re-read the Harry Potter books. I do, every now and then, just as I re-read other favourites, The Awakeners, by Sheri S Tepper; The Player of Games by Iain M Banks, It, by Stephen King; and so on.
But I don't always do this. There was a time when Guy Kay's Tigana was on the list of constant re-reads, but no more. I tired of it, I suppose. Lord of the Rings fell away a long time ago, after a dozen reads. Some stories stay with me and I'll get the itch to experience them again, while others are lost, or stay for a time and then fade. All of which brings me to a question I remember from my sadly far-off school days - what makes a great book?
My answer then, as now, is that a great book is one you revisit time and again. One in which you always seem to find something new, or an event to see in a new light. I know it's an incomplete answer, maybe a poor one, but it's as close as I can get. And it means that for each reader, the list of 'great books' will be different.
Isn't that refreshing?