I just finished the book

Having just read the book, I feel the film maker(s) did a good job adapting the book's unusual style to film.

The book, because of its collections of notes/letters style, featured more character development but the movie brought them to life by having most of the thoughts and musing brought forth as dialogue. To help better to drive the plot, some of dialogue was not spoken by the same character as in the book, and the timeline of some events were altered.

Now that I've read the book, and saw the film on TCM some months back, enjoying it very much. I feel I can say they both compliment each other; ie: The film is more enjoyable for having read the book and vice-versa.