Harry Potter and the Half-Blood Prince -- J. K. Rowling
I felt a little weird about it, to be honest. It didn't really click with me until about page 500--it felt like she was just going through the motions. It didn't really feel inspired until three-quarters of the way through. (Of course, there were fabulous moments of inspiration before that--Luna doing the Quidditch commentary was priceless).
But then I was completely blindsided. I didn't find WHO died surprising--it was HOW it happened that floored me. So much so that I'm going to read it again and I think I'll like it more the second time around.
I'm not going to write any more, because I'll end up giving something away. I'll leave the comments to be spoiler-land. (I'll start).