A direct adaptation would be difficult to do but the movie wasn't even an adaptation to begin with. It started life as an original script and the Director never read past the first two chapters of the book. As a movie on its own, it's an overall okay, but enjoyable B-movie. As an adaptation of the book it's terrible. It doesn't help that the Director passes it off as some sort of shitty satire of a book he has bragged about not reading.