I was thinking of interpreting this in two ways.
On the one hand, changing the book for the movie can be a bad thing. For that I picked the fourth Harry Potter movie and book. I felt this was when the movies were going downhill. They could have made it so great. Add more Quidditch, more party for the Yule Ball. Instead, we got Robert Pattison as Cedric, whom I never liked. When I saw him my first thought was "I thought Cedric was supposed to be hot". Plus Harry's hair! Seriously! The hair!
The second way we could interpret the task is if the movie was actually better than the book. The Devil Wears Prada is not a very good book. The movie I loved. You can read more about that in my review for the book. Just to sum it up, the movie is a lot of fun, the book is a whine-fest.