There are very few books I've read more than once.

I've read the complete Sherlock Holmes stories maybe 3 times. I find that, after an interval of 10 years or so, I can't remember how most of the stories end, so it's like reading them for the first time (sort of).

I'm sure I've read several of Shakespeare's tragedies multiple times: Hamlet, Macbeth, Richard III. (Is that classified as tragedy or history? It could be either, I guess.)

I'm sure I've read Huckleberry Finn at least twice.

I used to read a lot of SF, but I think A Canticle for Liebowitz is the only one I ever read twice.

Oh, there's Great Expectations and David Copperfield.

I guess I'm always hoping that the next book I read is the one that's going to unlock the mysteries of the universe, but I'm always a little disappointed, and that's why I don't look back.