I just got finished reading The Atonement. I didn't like it for the whole first half, because I kept wondering if the author was as mistaken about life as the characters he was describing.
The second half was much different than the first half (although they did go together), and all in all it was a good read, but I don't think I'll be going back to this author soon.
It does provide an in-depth "what if" scenario (as the whole book), and that is cool. It also has WWII atmosphere - like All Quiet On the Western Front, which I had to read in high school.
update 7/30/05: As I think back on this book, I like it more and more. It does go through a person's thoughts in a very similar way as The Brothers Karamazov does.