I said on a comment yesterday that one of the cliches of the Potter books is that the books “grow” with the characters – so the themes, situations and even language become more adult as they do.
One way in which this is definitely true in Order of the Phoenix is that Harry becomes the bratty teenager. It’s quite clever how JKR finds story reasons to make it seem like everyone is against him, life is unfair and to alienate him from his father-figure. Unfortunately it slightly falls into the “how do you write about boredom without being boring” trap. I know many people find Harry less likeable in this book. For me that’s true but the book itself doesn’t suffer. There’s still a lot going on that I like. Umbridge is a great pantomime villain (you love to hate her).