A marvel of a book. Well-written, engaging, and really quite impressive.
The most amazing thing about the book, for me, is the prose - McEwan is a master of free indirect style, a mode that blends first and third person narration (Flaubert is a master of it). This allows for this fantastic ambiguity, whereby you're not sure whether the character is really aware of all the things you are, despite the fact that events are being related from his/her perspective. Furthermore, it gives you this exquisite irony, these casual judgements passed on the characters that make you feel as if you know them better than they know themselves. It's gorgeous on its own, but is particularly suited to this novel, which could be summarized as an exploration of the ethics of storytelling.
I don't really have much more to say about it, honestly. I haven't decided yet if I'll see the movie. I mean, on the one hand, there's Keira Knightley, and generally, I'm sure that it'll be visually stunning, but on the other hand - re-read the previous paragraph and tell me if there's any way that film can convey that successfully.