I don't even know where to begin with this. As someone who has seen all the movies thus far and read all the books in one sitting because I was sick of not knowing the whole story, I was wildly disappointed with this film.
For me Half-Blood Prince is the best of the seven novels, and of the seven (since they are making Deathly Hallows into two parts) is really the only one that could fill out a whole film with ONLY things that matter. This for me was the deepest and most painful of all the books. The foreboding Rowling captures in this novel is quite astounding. It's that perfect moment in a series, like an eye of a storm, when everyone realizes what is really in store for them and has to choose a side and hunker down. The final act of this novel far outshines the inevitable ultimate battle between Harry and Voldemort. More death occurs in Hallows, but for me, the deaths in Prince were far more brutal and meaningful.
So, with that said, it's almost difficult for me to say that it was a bad movie, simply because what they did show was right on the money. It was beautifully shot, the performances were consistently stellar from all major players, especially Felton's Malfoy, who is scared and tormented, and Rickman's Snape who is nothing short of tortured in this film.
However, It was an empty shell of what it could have, and should have been. Epically hollow, if you will. I know the whole puberty thing figured prominently in the novel, but I didn't think they would devote quite as much time to it in the film as they did. Plus, really, I can't condone cutting the battle and the funeral. I just can't. And I can't believe they fucked up Dumbledore's death the way they did. The impact of his being gone was so much more significant in the novel, and that's just with my imagination to picture it.
There was nothing really wrong with Half-Blood Prince. But it just made it seem like the sixth book was merely a coaster for the seventh to sit upon which isn't the case if you read through them all. Plus, without introducing all the side-stories from this novel, really fleshing out Hallows will make no sense at all. It was gorgeous, it was, but none of it MEANT anything.
This film, for me, not only missed its mark, but felt like it didn't even know what the hell to aim at. By far my biggest letdown of the year.