Great Books of SF -- Reader feedback -- and a tentative defintion of SF v F

Part of an ongoing conversation:

Hmmm. DUNE, for me, does not stand up to re-reading. The only sympathetic character is Paul... at the beginning. By the end, I really don't much care what happens even to him. (And the sequels are unbearably oppressive - and worse, dull.)

It does evoke a sense of wonder, though, I'll give you that. There's some compelling stuff in there. I'm glad I read it. It just ...