Ok, so I actually don't have 101 reasons, and it's not that I didn't like the book, it's just that I'm extremely dissapointed.
I think this is the worst one so far.
This book needed at least another 50 if not 100 pages. I say this because there were so many scenes in which I would have liked to see more. For instance the apparition scenes, I would loved to have seen at least one more, the one in which Harry was able to apparate for the first time. I would liked to have seen another D.A.D.A. class, and maybe another one of Harry's classes, maybe some more quidditch. I think there were a lot of scenes that JK could have, or maybe should have written.
I feel like she rushed this book. In the first four books, there are many sideline stories going on, in this one, there is really only three(the war on Voldemort, the romance issues, and the Slughorn/HBP); Where as in Goblet of fire, for example, there were way more(voldemort/riddle house/bertha jorkins, rita skeeter, triwizard tournament, friend issues, school etc. etc...).
I knew this book would concentrate mainly on the Voldemort issue, but I didn't think that that was ALL that would be shown. This book was interesting and I like that the characters are older, but it seems as if JK was either too busy, too rushed, or just sort of short-cutted things.
I guess I just liked the books before this, because it was more than just war war war. The premise of the book says that while there is a war going on, life goes on. Well it would have been nice to see a bit more life and a little less war.
I guess there's this balance she has to write. She has to balance between darkness and light, War and Non-war, main story and sideline stories, and I think that this story just wasn't very balanced.
On other notes:
The ending made me cry like a baby, but then again I predicted Dumbledore would die by the end of Book 6 before book 5 was released. It's sort of a classic thing, the death of the mentor means the hero has to overcome great strife and still go on to win the battle.
I cried a lot for Snape, because I knew that a lot of people will take this to mean that he's bad, but I know he's really not. When Dumbledore practically begged Snape to kill him I was bawling so hard because I knew that Dumbledore wanted Snape to kill him, and not the other way around, him begging Snape NOT to kill him.
I was re-reading OotP, and Harry asks Nearly-Headless Nick about ghosts, what if Dumbledore comes back as a ghost? I doubt it, but you never know.
I totally had a squee moment when Draco was crying in the bathroom and Harry walked in. And THEN Snape saves him! :D Fangirly likey.
I whole heartedly believe that the last Horcrux is Harry's scar. I'm not sure how, but I'm almost positive Harry will die at the end of Book 7. It's a lot like Frodo actually, how can Harry go on after the journey's over? It's a bit like 'What's left once your part in the story is over?' Harry was targeted by Voldemort because of a prophecy, well what happens when the prophecy is fulfilled? Is Harry supposed to be married and live happily ever after? This would be ideal, but it all depends on JK, is she going to stay true and make sure he lives as intended because it's a pre-teen book? Or will it really become an adult book?
Oh, and ugh.... Harry and Ginny? WTF??? There was almost NO lead in into that. I like Canon Ginny, but it would have been nice to see a little H/G swoonage before book 6.(excluding Ginny's 11 year old crush) OH! That's another conversation that JK needed to write. I mean WTH? All of a sudden Harry kisses Ginny and then they're just together? It would have been nice to see what they had said to each other.
I'm also a bit sad that these books seem to have lost their magic. The first four books and most of book 5 were very magical, not just in the literal sense, but in the plot magic that all great books have. I sort of wish she had written all of the books and then released them, then maybe they wouldn't have seemed rushed or spoiled or what not.
On the whole I didn't hate this book. But if I had to rate it out of 10 stars, and give GoF(my fav) 10 stars, I would give this a four. I can't hate it, because it's canon HP, but I really think she rushed it. It just needed more in my opinion.
Also, if you didn't read my last post, I think R.A.B. is Regulus Black, and that he hid the locket in Grimmauld place, check out that post for proof of this.
</i>[Edit: I also just realized, maybe JK, after having the first three movies made, wanted to make sure that the last two books were filmable. *shrug*]</i>