I read CitR as an adult, and found it terribly painful read, not in the emotional sense but in the "God, when does this get better" sense. I've read Huck Finn about half a dozen times, the first time when I was about eleven or twelve, and it just doesn't get old. Bram Stoker -- I read his little collection of journal entries and memoranda in Jr. High and it still sticks with me.
It depends on what you mean by "YA" fiction. I think "YA" ends sometime in junior high. Madeleine L'Engle's great, but I would hope that by high school one's reading level would have advanced to Shakespeare and Hawthorne and Dickens and Austen and Hemingway and Faulkner (with a healthy dose of trash for cheap thrills -- Elmore Leonard, Nora Roberts, Stephen King, etc.). In other words, adult.
CitR is definitely at an "adult" level, but with subject matter only a surly adolescent could love.