I think you hit on it: Clarke’s fantasy is more literary than genre.

These days, my taste for fantasy/speculative fiction has become more refined; straight-up, empty-calorie genre fantasy no longer satisfies. I find spec-fic authors like M. John Harrison and Gene Wolfe (if the spec-fic/SF genre can lay claim to a “literary” label, Wolfe has certainly claimed it) much more engaging to the mind. If Clarke is anything like them, then I think my reading taste has now matured enough to appreciate her.