I sorry to say, but I preferred the movie over the book. They had similar story lines but there were slight variations. There was the German possession of Joey, where the two brothers looked after Joey and Topthorn. I thought that this part was better than the book. Also the part with Emile, as in the book, she looked after the horses for the Germans, while in the movie, she hid them from the Germans. Also, the movie was not told in Joey's view, so it was possible for them to make things happen to Albert, like the gas attack. Over all, I thought that the movie was a whole lot sadder, because I cried in that, and I didn't while reading the book.
I was really annoyed how Joey was like a super genius and knew every single world in the English language. I really don't think horses are linguists as well, because Joey could understand English, German and French.
In all, this book was a great work, but the movie is definitely worth watching.