The Book vs The Film
Novel written by Aron Ralston & Film directed by Danny Boyle
Throughout the novel, Hosseini emphasizes that redemption and forgiveness can be achieved through true remorse and care for those affected. The main character, Amir, feels overwhelmed with guilt when he does not stop the assault of his family's young servant, Hassan, and strives to redeem himself by standing up for what he believes is right and finding Hassan's rapist.
In the book, Hassan has a cleft palate (deformation of the lip) and in the movie he does not. Because he is a Hazara, Hassan is already considered to be an inferior in Afghanistan. However, his deformation makes others think even less of him. In the book, there is a significant section of the story dedicated to correcting the deformation. Amir's father, Baba, pays for the surgery which ultimately makes Amir feel more guilty when he abandon's Hassan. This scene is critical to solidifying the relationship between the two boys and in the film version makes Amir's regret seem less powerful.
Assef was less interesting in the movie
Assef, in the novel, repeatedly mentioned his loyalty to Hitler and his beliefs. However, in the movie, he never brings it up. The novel portrays him as psychotic and somewhat insane while in the movie, he is not nearly as complex of a character. His love for Hitler makes him seem far more wild and crazed than his movie counterpart. He also wears brass knuckles in the book, but is not wearing them in the movie. Because of this, the scene in the movie where Amir confronts him feels less intense. In the Novel, Assef is truly something to fear and it makes Amir's journey to redeem himself more climactic.
The Movie was less Graphic
In the novel, the scene in which Assef assaults Hassan is disturbingly detailed and graphic. Of course, this scene had to be heavily changed and censored to be appropriate for a film. In the movie adaptation, we don't see what is happening and the details of the assault are mainly implied through the audio track and very short video clips. While this does an effective job at expressing the psychotic nature of Assef, it does not give the story the same sadistic, pessimistic tone seen in much of the novel. Because of this, in the novel, Amir's path to redemption is more emotionally intense.
The Movie shows less of Hassan's Adult Life
In the movie, the viewers get a much briefer glimpse of Hassan's life as an adult. All the film viewers really find out is that Hassan dies. As a result, the viewer does not ever get a chance to understand how the assault affected Hassan's long-term mental health. In the novel, this section makes it easier to understand why Amir is so determined to set things right, but in the film, the path to redemption mainly is based on short-term character changes.
The novel was more emotionally exhausting
I personally felt like the book had no place where the reader could relax. The author repeatedly beats the reader down with a succession of depressing scenes and expressions of Amir's regret and self-hate. The movie has numerous "resting points" and calm, artistic scenes such as the kite flying scene. This has the effect of making the movie far more easy to tolerate. While I found these breaks to be refreshing, it places less emphasis on Amir's personal guilt and disgust for his actions. His process of redeeming himself in the novel seems to be far more difficult.