A book you expected to dislike that you loved? One you wanted to love, but couldn't?
I reluctantly read The Thorn Birds in a county jail, as it was the last book on the library cart when it came round to me. From the cover to the blurb on the back, it not only didn't interest me, but begged me not to read it.
I enjoyed that book so much that I've read it twice since. Was thinking I might read it again soon.