I forgot to finish my point!
These characterizations from the book are so much more nuanced and interesting, and they support a more intriguing theme than the characters in the movie (and it's not like it's hard for movies to have nuanced characters...)
The movie has always been, to me, overly concerned with making sure that we know that Howl, Sophie, Calcifer, and TWoTW are good people who should be loved. The book is far more willing to say, "hey, they're people: they're complicated, really complicated, and kind of annoying and some of them are just messed up, but a few of them are worth it. And you are worth it, even if you're complicated and little messed up too."