1. The movie is 2.5 hours long, and I didn't notice it. This is because there's practically no time to regroup, as the movie tries to fit as much of the book in as possible. I'm pretty sure there are a few things I wouldn't have understood if I hadn't already read the book.
2. The Order of the Phoenix is my second favorite of the series, behind only The Prisoner of Azkaban. As such, I probably knew somewhere in my brain that I'd be a little bit disappointed. And I was. The book is so dark, from beginning to end. Harry is losing it and lashing out at everyone around him, and pretty much being a prototypical self-absorbed 15 year old jerk, while everyone else is grim and depressed because instead of fighting Voldemort, they have to fight the Ministry. The movie didn't even come close to conveying the total feeling of despair that pervaded the book, and didn't really explore the more adult themes. Which is somewhat understandable, seeing as how they were on a mission to cram as much stuff into 2.5 hours as possible and wanted to keep it appealing to smaller children, but I still missed it.
3. The entire time, I was holding on to the very, very slim hope that my favorite scene from the book would make it into the movie. Since the scene is almost entirely superfluous, I was pretty sure it wouldn't. I was right. That scene: When Harry, Hermione, and Ron visit Arthur in the hospital and run into Neville visiting his parents, and an addled Gilderoy Lockhart. Gilderoy Lockhart is easily my favorite character in the series. Only Dobby the House Elf and Severus Snape come close. This is odd, because The Chamber of Secrets is easily my least favorite book of the series.
4. Speaking of Severus Snape, I'd like to say that Alan Rickman is awesome. Also, I hate to spoil the last book for everyone, but Snape is undoubtedly a good guy. Why? His hair. It's dark. Every male character with blond hair is a villain, and, to my knowledge, there is only one dark-haired villain. Gilderoy Lockhart: Blond. Lucius and Draco Malfoy: Blonds. Peter Pettigrew: Officially "Thin and colorless," but portrayed as a dirty blond in the movie. Technically, Ian Hart, the actor who portrayed Professor Quirrell, is dark-haired, but Quirrell wore a turban at all times and had Voldemort sticking out of his scalp, so I think his case should be thrown out. (Update: Barty Crouch was blond too.) Personally, I thought Lupin was the only exception to the "Blond hair = Evil" rule, but Rowlings specifies his hair as "graying light brown."
The dark-haired villain is Tom Riddle. Note that when he becomes Lord Voldemort, he loses all his hair. His hatred of dark-haired peoples, even though he himself is dark-haired, mirrors his hatred of all halfbreed wizards, even though he himself is a halfbreed. Thus, there can be room for no other dark-haired male villains. Snape is a good guy.
If I had the time, then I would research a corresponding theory that black haired women are evil, which suggests that Narcissa Malfoy is actually going to be a heroine as well.
One more week, everyone. One more week.