Moving right along in my quest to read the entire 7 books of Harry Potter! I am now on the third book, Harry Potter and the Prisoner of Azkaban.
It's hard to know what to say when I've read all these before, except to comment about the things that are different about the movie. One thing I definitely have noticed, however, is that J.K. Rowling does an excellent job of dropping clues about what is going on -- except you don't notice it when you're reading the books for the first time.
*** Warning: I'm about to reveal something that may spoil the book (or movie) for you if you haven't read (or seen) it! ***
For instance, in the third book Hermione has enrolled in more classes than she could take in a normal 24-hour day, so she is using a time-travel device to attend them all -- but you don't find that out until the end. However, odd little things are constantly happening, like Hermione suddenly being in class when Ron and Harry didn't see her walk in, or Hermione carrying books for classes she doesn't have that day. If you already know what is going on, you really pick up on these things -- but if you don't know, some of them slip by you.
In other words, J.K. Rowling is a MASTER of subtlety!