I think it was the constant suprise that tbe writer gave us. We all pretty much agreed that it was hard to see things coming. When books aren't predictiable...that makes a good book.
I believe the Kite Runner has been so popular with book clubs for a few reasons. It is about a culture many of us are not familiar with so the description of life in Afghanistan (before the Taliban) was compelling. How people had to flee their homes and everything they owned to get out of Afghanistan was heartbreaking. And then, the people who managed to escape had to pick themselves up in a new country, learn a new language, and find a way to earn a living. Courageous and sad and heartfelt all rolled in one :-)
Most of us have witnessed something bad happening and not intervened at some point in our childhood so we could kind of understand how what Amir witnessed happening to Hassan shadowed Amir's life. The kite fighting was also well described and paralleled the storyline. Overall, a well-written book with likable (mostly) characters and an engaging story.
I think the characters in "The Kite Runner" are what makes the book such a favorite for discussion groups. We talked a lot about Amir's relationship with his father and how it evolved. Also Amir's growth was interesting to watch as the book progressed. We also liked learning a little about recent events in Afghanistan as well as the Afghan culture.
The singer, Clay Aiken, suggested The Kite Runner to his fans on his official fan club site. He read it on a plane and said he found himself yelling at the book to the consternation of his fellow travelers. His suggestion started a very long, exciting discussion which went on for about 80 pages until it died a natural death. What a great book and what questions it raises for discussion.