Let me just begin by saying that out of the six published HP books, Order of the Phoenix is my least favourite (favourite's a tie between Philosopher's Stone and Half-Blood Prince currently). Thus this adaptation is one that I really haven't been on the edge of my seat for. Besides which, even as my least favourite book, I knew the film wasn't going to be anywhere near as good. OotP was nearly seven hundred pages long, and trying to cram all that into a two hour film was just not going to work. As a result, I felt a little miffed at the way the film progressed, since it seemed to deviate a lot more from the book than previous films have in terms of explaining things and advancing the plot along.
Lupin and Sirius' first scene was great. Ahaha, they shacked up rather nicely by the look of things. It's funny because I spent most of the first PoA viewing absolutely despising David Thewlis as Remus, and yet after a second viewing and in this film, I've really come to like him quite a bit (awful mustache not withstanding). That terrible, lost look on his face after Sirius disappeared through the arch was a little heartwrenching.
However, the problem (and this applies to a lot of the other supporting characters too) is that Remus barely got the screentime that a character of his importance merited. The other members of the order seemed sorely underused too. Brendan Gleeson seemed to be phoning in his part in places, which was sad because he was so enjoyable to watch in GoF.
Who else does this rule apply to? Lessee...Percy Weasley (why was there nothing on his feud with the other Weasleys? We weren't even explicitly told that the tall redheaded PA with Fudge was Percy!), Dumbledore (until the climactic battle, it felt like Michael Gambon was phoning in his part too). Trelawney. I mean, you cast an actress as awesome as Emma Thompson and then decide that she's going to be in the film for a collective two minutes? Seriously, WTF? Maggie Smith was also sorely underused as McGonagall. And Tonks who, I must concur with moony_girl13, was really hot. I hope we see more of her in the HBP film.
On the flip side, they really emphasized nicely the idea of the lead trio as part of the larger group of students. Neville got fleshed out much more, and the actor who plays him (can't remember the name right now, dammit) did that very well. Luna was just adorable, and had a lovely Irish lilt in her voice.
Given that there was much focus on her as an antagonist, Imelda Staunton made a completely despicable, nasty and wholly evil Umbridge, and watching her in the role reminded me of how much I hated the character when I was reading the book. Spot on portrayal.
Helena Bonham-Carter appropriately had a case of teh crazy as Bellatrix. I remember thinking she was a little OTT during the film (did there need to be cackling?), but in retrospect it was enough for the short time she was onscreen. I was also quite surprised that Lucius Malfoy was onscreen as long as he was (not that I minded, because Jason Isaacs and his fabulous pimp cane were seriously *phwoar* as per usual). Didn't see any reference to him being arrested after the ministry battle though. I assume that there'll have to be some nod to that in the HBP film if they want to keep the Unbreakeable Vow scene between Narcissa and Snape in.
Speaking of Snape....wellll, he felt a bit underused too. Alan Rickman was brilliant and lovely as ever though (I will never get over that amazingly sexy voice of his, NEVER). The little scenes he had with Umbridge were quite entertaining. The occlumency lessons with Harry were good too, though the MWPP flashback was really too brief.
I would've loved a Kenneth Branagh cameo/return appearance as Lockhart. Still, I guess that scene really couldn't fit anywhere in the film and Branagh was no doubt too busy to do it.
How did Flitwick become a choirmaster? Did he give up teaching Charms? Anybody? Bueller?
I had been hoping that Aberforth Dumbledore would turn up somewhere, and he did. Complete with goat. *SPORFLE*
I hope that the HBP film will be better than this, but I'm not so sure. Long books like OotP and HBP don't tend to make great adaptations.
Should mention that the trailers before the film looked quite good too. Especially Stardust. I wasn't all that enthused about it, but upon seeing the trailer? Y HALO THAR PETER O'TOOLE AND RICKY GERVAIS. Definitely seeing it now.