*** Warning: This review contains spoilers! ***
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I didn't understand why Harry wouldn't tell Professor McGonagall about the corporal punishment that Umbridge was inflicting on him in detention. And why didn't Harry speak up earlier about what happened in the graveyard? He could have saved himself a lot of angst. Probably lots of people didn't believe him because he never spoke in detail about it, which could reasonably be interpreted as suspiciously defensive behavior. When Hermione led Umbridge into the Forbidden Forest, I understand that something had to be done about Umbridge, but I can't help but feel that the centaurs and Grawp were all very ill-used! I can't believe that Harry, Hermione, AND Ron all forgot that Snape was in the Order, and why did J.K. Rowling introduce the two-way mirror in this book in this way!? UGH! That was worst part - if Harry had opened the mirror earlier, he would have had a simple and easy way to communicate with Sirius, and the whole Department of Mysteries fiasco could have been avoided, not to mention Sirius's death. If J.K. Rowling wanted to kill off Sirius, couldn't she have come up with a way to do it without making it all Harry's fault? Or was there some reason that she wanted readers to blame Harry?! Anyway, it also seemed to be a real shame that all those prophecies in the Department of Mysteries got destroyed. And lastly, I can understand why Dumbledore didn't want to tell Harry about the prophecy, but how hard would it have been for him to EXPLAIN why Harry needed Occlumency lessons?! Sigh.
On the bright side, this book did do a good job developing Ginny's character. Finally we see evidence that she was smart, funny, a good Quidditch player, and a powerful witch.