My friend and I saw Atonement today. The movie made me cry, whereas the book left me in shock, and some outrage once I finished it. Even though I knew how it was going to end, I still cried. James McAvoy may very well be my newest favorite British/Scottish actor (he was halfway there with Last King of Scotland).
Considering how I knew the story, there were few surprises in the movie for me--but I still enjoyed it and want to see it again. The exception was the musical score. I loved it. The click-clack of the type-writer has never been so musical and melodious.
If you're on the fence, wondering if you should see the movie or read the book first, I think I'd recommend the movie, which did a fairly good job of staying loyal to its source. Visually, it is beautiful and the acting is great. The book can be too wordy at times and dwell on minutiae, which even I occasionally got impatient with. Still, I enjoyed and recommend both.