It is not uncommon for books to be considered better than the movies on which they are based and the Harry Potter series is no exception. In the book, there is always much more character development and the characters are portrayed differently in the movies.
For example, Peeves the Hogwart’s ghost doesn’t appear in any of the movies and according to the books, Mrs. Norris should have been a scrawny “dust-colored” cat with yellow eyes but in the movie, she was not scrawny, her eyes were not yellow and her fur was brown and grey. Because movies have a time limit, they have to leave a lot of scenes out. Another reason is that books have the advantage of describing things in great detail and you can hear Harry’s thoughts where the movie doesn’t permit as much detail or allow for time to “hear” Harry’s thoughts.