While the characterization of Harry Potter himself is pretty much consistent between the books and movies (with a few minor but critical exceptions), the characterizations of his two best friends, Ron Weasley and Hermione Granger, are spotty at best. In most cases, Hermiones character is glorified and aggrandized, usually at the expense of Rons. This may seem relatively unimportant in the grand scheme of things, but in an unfinished series, such as Harry Potter is, it can be extremely important. If the characters are fundamentally different in the movies than in the books, future actions may not have the proper groundwork to be believed. Moreover, the way these characters are portrayed in the films has had, I believe, an impact on the way these characters are viewed even to those who have read the books.