But why blame just him? You didn't like the film, that's fine, but don't blame just the director. It's a team of people who are involved, such as the cinematographer, editor, composer etc.. If you are unhappy about the changes and cuts, then Michael Goldenburg (the screenwriter) is the man on which to lay most of the blame.
Personally, I think he is a great director. Obviously not in the same league as others such as Del Toro, Nolan, Cuaron, Burton.... but he is a very good, versatile director who has produced stunning pieces of art (HBP) and expressed a political theme which mixed in with the magic (OOTP). Considering he had a 800 page book to adapt and only had experience with TV films when he entered OOTP, he did a pretty good job.