I enjoyed it. I didn't think it is a classic. With speculative fiction (science fiction, fantasy), I'm always concerned whether an author creates a robust, consistent world with the fantastical elements. I want something I can believe in after I've taken the initial leap of faith into the story by accepting the author's premise. I don't want my patience, good will and faith stretched too far. In this book, I think the author creates a believable approach to the concept of time travel. The two lovers are sympathetic characters. IIRC, it was a little confusing at first while the time traveling element sorted itself out, but if you are a patient reader that problem resolves itself.
My only caveat is that I was a little disturbed by the element of romance in an adult-child relationship. There are all sorts of ways to justify it and sanitize it (and if you read reviews, you'll see that many people have), but it remains a little icky to me.