The book is fantastic, I’d recommend reading it one way or another. ;) Speaking personally, I lose some motivation to read a book after seeing the movie. But book-based movies of course rarely if ever live up to the book. I read first, so I can’t speak to the other way around, but I think I was looking forward to the movie a lot more than I would have if I hadn’t read the book. I also suspect I was more forgiving of the movie than if I’d seen it cold.