Been years since I read Asimov, but I remember his stuff being right up my alley in terms of readability. Characters talking in front of a cardboard background, bouncing ideas off of each other, like a sci-fi Jane Austen.
Tolkien's at the other end of the spectrum. I've made half a dozen serious attempts to read the LOTR books, and get smacked around by the prose every time. He starts to paint a word-picture of a dell or grove or something, and I'm done.
For whatever reason, I run into a brick wall when I read physical descriptions of the scenery. Any genre, any reading level. I start to zone out and skim the words without really processing them. I bet there's a quirky psychological disorder I could self-diagnose based on this.