Re Dune, I must say that while I thought the first book excellent, as the series progressed, I liked it less and less, and stopped reading after the fourth book.
Yes, it gets worse... I think that I am still in love with the Duniverse because it reminds me of the comfort of my youth as a reader. I still remember the days I read the first books in my bedroom. I finished the original Dune in two or three days, and I was so moved by the experience that I immediately began reading the next volume... and then the next.
The only two other novels that caused so much stir in my soul are Umberto Eco's "The Name of the Rose" and "Focault's Pendulum"