As the franchise progresses, the directors of the Harry Potter movies have had to deal with a bigger book each time, resulting in every movie being longer than the last. Despite this, with movie four being around 2 and a half hours, many fans still complained about the way the movie missed out on huge portions of the book.
In defense of Michael Newell, I have to say, that he has indeed created a good, maybe even great, film. What fans of books and comic books don't seem to realize when they go to watch the feature film adaptation is that the movies are not made exclusively for them.
The director and studio have to assume that the audience is not familiar with the franchise the way a die-hard fan is, and therefore make a movie that displays the story in a format that this audience can understand, and also appreciate as a movie itself. This means the movie can't go on for 4 hours, detailing as much of the book as possible.
Keeping the audience's interest is hard as it is beyond an hour and a half, and Newell has made a movie that maintains the momentum for most of its two and a half hour length. Considering these constraints, Newell has made a fine movie, having chosen very carefully what and how much of the book he would translate to the screen.
Personally, I would have preferred a movie that spent as much time on the interaction between the various characters, and the way their relations change in the story, as the film spent on detailing Harry's escapades. Newell had to cut down such relationship events, like Harry and Ron's fight to a very few short scenes, simply because there wasn't enough time.
And this is where I think the Warner Bros. might fail the fans. Having a different director for each movie does give us fresh views of the characters, and shows us the different dimensions of the stories, but it also eliminates the possibility of a 'for-fan's' movie on the DVDs. At the end of the seven movies there won't be one single director to wrap up the whole thing, so it is very unlikely that fans will get the movies that we wanted.