There is a good reason why critics have been raving about this movie and given it more Golden Globe nominations that any other film-- the acting is superb, the plot interesting, the cinematography excellent, the score moving, and it deals with a very substantive matter, indeed a matter of Biblical proportions-- atonement. This movie is at the other end of the spectrum from what one might call 'fluff' or 'mere entertainment'.
... I do highly recommend this movie. It's like drinking strong coffee, even when you don't need sobering up about the world's realities. I wish some of the characters in the film were a bit more likeable, but then, they are 'true to life'. If you ever need the nonsense about all human beings being basically good knocked out of your noggin , or the nonsense that everything will turn out alright in the end if you try hard enough to atone, whether or not one repents of one's sins and seeks God's help, then this is the movie for you.
Read Christianity Today's Movie Review of Atonement