Harry Potter and the Order of the Phoenix is nowhere as good as Goblet of Fire. It's kind of engaging: eventhough it's very long, time passes easily. However, the atmospheres are just copied from the previous films in the series, especially Prisoner of Azkaban, which was not the best one to boot.
Maybe I'm tired of always seeing the same Hogwarts shots, and maybe I'm tired of being reminded that the courtyard of Hogwarts is actually in Christ Church College, Oxford... but really, I wasn't all that thrilled. Not that it is a bad movie, but after all the emotion of GoF I expected way better. Or maybe it's just that I need to see Potter movies with Rahvin to really enjoy them.
More details: the battles are really a bit too much Star Wars, especially Dumbledore vs Voldemort at the end. Also, the humor is overdone in points: Snape, for example, has turned into an entirely comic character, which is done on purpose, and while it was good when it was kind of one-offish in GoF, it is not all that credible when it's done routinely in this one. Snape is supposed to be a central tragic figure, not the one who provides comic relief. Ron, who is more cut out to do that, sometimes also does, and a couple of jokes are good, but really, nothing outstanding.
The breast enhancement photoshopping for Hermione was actually there only in the final scenes (I hear that it's been canceled from the movie posters because of feminist pressure groups in America). Luna's characterization, although hailed as perfect by reviewers, was alright but nothing special. Grawp actually has GW Bush's face, which is fucking stupid in my opinion. And Lucius Malfoy comes across all queer, but/since he's got the best leather top ever.