Two favorite books of mine I've seldom seen mentioned but I think are gems: The three stigmata of Palmer Eldritch and Time out of joint, both by Philip K. Dick. The first plays with several layers of reality along the book. One time I found myself re-reading some passages because there were so many layers it was hard to follow, but it's worth it. The second is (if I recall correctly) the inspiration for a 90s pop movie starring Jim Carrey. I won't mention the name because it might give away some plot points.