I will tell you exactly why this movie is painfully bad...

Rating: 1/10 (25 April 2008)

I will not say that this is a really bad movie because a lot of people think it is really good and, unlike some others, I am not arrogant enough to think that my taste should set the standard for everyone else. There is no accounting for taste, even bad taste.
However, I thought it was a painfully bad movie and I will tell you very specifically why.
First, some specific things that prevented a knowledgeable viewer from sympathizing with the characters.
1. In the promo they say that a young girl sees something she doesn't understand and mistakenly tells a story that that has tragic consequences. That entire sentence isn't a quote, but "something she doesn't understand" is. In fact, she sees several things and she does understand enough to know what is going on. The specific event that tops off the sequence of events that ruin lives is one she knowingly lies about whether or not she fully understands it, and she clearly has set out to destroy a man's life (apparently motivated by jealousy). Even before the "main event," she says that he should be put away where he can hurt no one.
2. It is said in one of the promo trailers (no spoiler here) that Robbie had the choice between prison and going to war. Well, this was a part of WWII that most Americans don't know about because America hadn't entered it at that time, but all able-bodied men in the UK went to war.
3. The scene in the library was absurd. To disrespect one's family by doing something like that in a library with a horde of people wandering around would have been the height of disrespect and stupidity.
4. In the 1930's in Britain (or America for that matter), if a father caught his daughter engaged in (or learned of) the acts that actually did occur the boy would find going to prison to be one of the nicer things that might happen to him.
Now, about the structure of the movie:
The story has a beginning and an end. Most of the story should have taken place in a middle that does not exist in the movie. There are events with major consequences for all involved: the girl (Briony), Cecelia, Robbie, the Tallis, Quincy, and Turner families, as well as others. These events take place in the beginning of the story: And the consequences? We learn nothing of what happened except a little of Briony, that Robbie chose war, and that Cecelia stayed around, possibly waiting for Robbie  or possibly not, as we learn near the end of the film. The middle of the story is related in a few sentences.
The end of the film is supposed to show the "atonement". Presumably, this is Briony's atonement for ruining a few lives  we don't know how many because that would have occurred in the middle of the story. Atonement is "satisfaction given for wrongdoing." Unless one includes satisfaction obtained by the wrongdoer, which I don't think counts, there is no atonement.
So, what does one have? Some very unlikable characters, some of whom have bad things happen to them because of bad things done by other unlikable characters. The few likable characters disappear during the non-existent middle of the story.
If you choose to see this movie you may very well find something to like, but I don't think it will be anything that is a part of the story.