It's a good book. I always think about ways that books could have been written better, and there are some things in Book 6 that I wish had been different, but it was just about as good as it could be under the circumstances.
The Harry Potter books have always been a mix of "British boarding school novel" and fantasy, as well as a mix of charming humor and dead-serious conflict. J.K Rowling always had to walk a fine line in order to "pull it off". I think at this point in the series, the mundane boarding school issues and the inconsequential bullying and the "who's going out with whom" and a lot of the throwaway humor will have to be pushed aside to make way for a really good story about Harry Potter's date with destiny. I think that was evident in Book 6. For example, Draco Malfoy, while still a priggish little snob, was a much more serious character. He wasn't just a bully or the butt of a few jokes; he actually had personal conflicts of his own, and perhaps he deserves a little of our sympathy for a change.
Book 6 also didn't have as many plot twists and surprises as the earlier books, with the main exception of "Who exactly is the Half Blood Prince?" I hate to say it was obvious to me, so let's just say I had a really good hunch the first time the Half Blood Prince was mentioned. But I will concede that it was
supposed to a be source of real intrigue in a book that didn't really have that much, especially compared to the earlier books. I rather enjoyed this kind of fresh new narrative arc.
On the other hand, it did take 80 pages before Harry met up with Ron and Hermione, and even after 200 pages I felt like nothing had really happened besides expository dialogue. I was little bit put off by that. But if you're not finished with the book and you feel the same way, let me assure you that by the time you've read about 500 pages, you'll be saying, "Boy, when this story really gets going, it REALLY gets going."
I suppose my biggest gripe is that, despite the build-up for most parts of the story, some events happen too suddenly for my liking. For example, when a character first realizes he's in love with someone, it seems to happen totally out of the blue. I realize that love can seem like that sometimes in real life; however, in real life as in books, love is usually preceded by some sort of contact with the other person. When love first rears its head in the book, that's when we're told, "Oh, by the way, these two people spent a lot of time together over the summer," and the book devotes about two sentences to it. From that, we're supposed to feel like this feeling of love is perfectly natural and spontaneous. I'm sorry, but to me it seemed a little too arbitrary and self-conscious, as if the author was mainly trying to please her fans. I would have preferred a more detailed narrative of the events that led to the characters' love. When they're together during the summer, tell me about some of the things they do together and how they feel about each other. Maybe they collided in mid-air while they were playing Quidditch and ended up in a heap together on the ground and laughed when they looked into each other's eyes. Maybe one of them felt a tingle when they brushed hands when one was passing the salt to the other at the table. Maybe one of them felt really disappointed on the Hogwarts Express when it became apparent that, after spending so much time together during the summer, they were going their separate ways back in school. Okay, that last one really is in the book, but tell me more about why it's significant when it happens. Otherwise, it's just a little clue to something that happens later, and what happens later feels a little too forced. And I still wonder what they did that summer before(?) they fell in love.
At least let one of them obsess about the other's hair or something before they fall suddenly and madly in love.
SPOILERS
There's one little heart-warming touch I'd like to mention, and I hope it's not a big spoiler. In Book 5, everyone thought that Hagrid was wasting his time with his half-brother Grawp, but in Book 6, Hagrid is completely vindicated. It made me remember what he said tearfully in Book 5: "He's my brother. I have to try." Good for Hagrid.
Speaking of giants, for those who've finished Book 6, did something remind you of Yaga-Shura from Baldur's Gate II: Throne of Bhaal?