The Kite Runner
One major scene that was actually in the film and not in the book was when Amir's father, Agha Sahib, collects dirt in a small container before they leave Kabul, and then kisses it. It's different from the book because in the book, he kisses the ground. I think this adds to the entire story though because it shows his love for the country and how he will miss it. Also, later on the film, when he is sick, Agha Sahib looks at the container again, remembering and missing the land he knew.
A scene that was not in the film but in the book was when Hassan and his father are leaving, and Agha Sahib gets down on his knees and begs them to stay. I think the filmmaker wanted to create an Agha Sahib that was more quiet. This scene was however, integral, because it showed Agha Sahib's weakness and how he needed and loved Hassan and his father.
A major scene that was not shown entirely in the film was the rape scene. But for viewer reasons, it couldn't have been shown. Also the film is rated pg-13 so it still has to be somewhat appropriate. But the film still did justice to the horror and powerlessness of that scene. It really showed the cruelty of Assef the same way the book described him to be.
The film did not show the part where on Amir's birthday, Assef hands Amir a book about the biography of Hitler. This was an important part of the novel because it showed Assef's character as cruel and domineering, someone who looked up to Hitler. But for timing reasons, the director would have to pick and choose certain things to cut out and include. But I still feel like they could have included that in the film because it still shows Assef giving Amir a gift.
Another part I think the director took out for timings purposes is when Amir and his wife, Soraya, cannot have a baby. This was important because it contributed to Amir wanting to find Hassan's son, Sohrab. But the film would have been very long otherwise because many scenes were short.
Something else which was an integral part of the novel was Amir's thoughts, which weren't entirely shown in the film. The reader comes to know Amir and his character much more from the novel because it is written from Amir's point of view. However, the film would not be able to show thoughts unless there was a background voice over, which would have been difficult to fit with the scenes.