Obviously, if you read the book, you are going to (or already have) seen the movie. Many sub plot points from the book were consolidated or condensed (even with a run time of 153 min), and parts of the ending were omitted, but overall I think it worked.
I think there might have been some parts that come out of left field for people that haven't read the books, but having read the books, I understood.
If you are a fan of the Potter series (books, movies, or both), you should see this. If you haven't seen or read any Harry Potter, try watching the first movie, and if you like it, continue and then watch this one.