Dune, Dune Messiah, Children of Dune, and God Emperor of Dune were excellent, some of the best sci-fi I've ever read, very impactful, superbly written. That being said, Heretics of Dune was just ok and Chapterhouse stunk. The first four were just superb.
I found Lord of the Rings, particularly the HOOOOOORRRIBLY boring and banal Tom Bombadil junk and the poetry to be tough to get through. That was tough. The Two Towers was more boring than an insurance seminar. Return of the King, awesome, though seriously lacking in violent battle details! One thing that Tolkien stunk at was the details of battle. So vague, short, and bland were the battle 'scenes' of his books. Thank God for the films!
As for Lewis' Narnia books, I'd rather have a colonoscopy! But I like Lewis' theological stuff, though it's hard to read like Chesterton, but very powerful
I endured Dune. I just could not see the appeal and have never picked it up again.. but I could NOT put down LoTR the first time I read it...and I was only 12 years old at the time.
I agree with elfdream. I did make it through DUNE, DUNE MESSIAH and half of CHILDREN OF DUNE before I had an intense urge to run around turning on all the faucets and playing in the water. It sort of poisoned Herbert for me.