There are a number of little things in the book that rub me the wrong way, including...
- I feel that this book ignores a lot of the established characters. It's the least we see of the Dursleys in the series. Neville only gets mentioned twice, when he used to be a character who shows up every 1-2 chapters. Luna gets three appearances. And Professor Snape! He's been trying to get the Defense Against the Dark Arts teaching position for at least 20 years. Now he's finally achieved his life's goal, and...the book does nothing with him. He teaches one class, and that's it.
- Non-verbal spells are now standard? What?
- Harry becomes completely obsessed with Draco Malfoy's scheme. I didn't like that much in book 2, and I don't like it much here's. I thought it was weird and creepy for Harry to use the Marauder's Map to spy on Malfoy constantly, and Harry escalates it by ordering Dobby to spy on Malfoy all the time. Harry, jeez, calm down.
- Harry's major infatuation with Ginny was sudden and came out of nowhere.
- Can I just say that Malfoy's plan to bring Death Eaters into Hogwarts was long and convoluted? Yeah, I know, that's par for the course for Voldemort's team, but still. His plan to kill Dumbledore was also pretty half-hearted. He could have easily asked for a private meeting with Dumbledore, since he's a prefect, and killed Dumbledore directly.
- Dumbledore is supposed to give Harry lessons on how to defeat Voldemort, but really, all he does is show Harry some of Voldemort's old home videos. Don't get me wrong; it was interesting to learn all about Voldemort's backstory. But it didn't seem particularly relevant to the problem of "Voldemort is trying his hardest to kill Harry". As we'll see in the next book, the lessons were utterly useless and did not help Harry in finding or destroying Horcruxes.
- I think one unavoidable problem with this book is that it takes place at school, where everyone is totally isolated from the war. I wanted to hear more about the war and stopping Voldemort; I'm not as interested in hearing about Quidditch practice. The book starts with the two prime ministers meeting each other, which set up false expectations for me; they end up being unimportant characters who never appear again.
It's not necessarily a BAD book. I'm just saying, a lot of little things bugged me, and overall, it felt sort of like a placeholder book.
I wrote a chapter-by-chapter parody of this book. I thought about doing one for the other books, but that would take too much time.