DUNE is very focused on the interior lives of its characters, and thinks it's a LOT smarter than it is. Just like Zen, and to a large degree something like Narnia or LotR, you just have to encounter it at the right age. I can't imagine someone who has never seen the movies starting to read Narnia at age 32.

They're classics, of course, but they definitely have a specific age around 15-21 where they hit hardest. "Early Adult" books, maybe?