The Knife of Never Letting Go by Patrick Ness
This was heavily recommended to me by a friend. It was a bit awkward getting into it, stylistically, but when it had me hooked, it had me hooked. It's exciting. And interesting. There's plenty of stuff to think about, and like my favourite science fiction, it's got an idea at the seed of it that's intriguing. And we get to see various ways of it playing out - some more tragic than others.
I don't want to spoil anything, because the story keeps its secrets so well, and you want to be suprised. The only thing I wasn't so happy with was the ending - it's a quite shocking change, and I'm almost angry at it. It's an ending that says there's going to be a sequel (as opposed to simply being abrupt but natural). In fact, I think I would have preferred it to have ended half a chapter earlier, and not given me that unpleasant shake, whilst still being a satisfying ending.
So I'm a bit annoyed, but really, I enjoyed the book so much I'm not going to hold it against it, and I'm going to recommend it to everyone, and I'll sit here impatiently waiting the second.