Nota Bene: I can only review the book as someone who had seen the movie first.

That said, the book and the 2002 adaptation are quite different. In setting, in theme, in the portrayal of the characters, and in many other areas they differ quite a bit.

Not that that makes either of them not good. (minor spoilers follow) The movie is a romance, primarily is an adventure story, and takes place primarily in Africa. Harry Feversham (Heath Ledger) is the main character and the focus is on his journey to reclaim what has been taken from him via the titular four feathers. The book is much more interested in the psychology of its characters, is primarily an exploration of its characters motives and thoughts, and takes place mainly in Great Britain. Harry is still A main character, but is by no means THE main character. Others, namely Colonel Durrance, get much more time to shine.

The verdict? I think I preferred to experience them in this order: movie first and then book. I feel like I would have been disappointed by the movie's choices in adapting the story, whereas this way it's easier for me to appreciate them separately and for what they are. I like them both and would recommend them to those that I think would enjoy them.