The title suggests, I am not impressed at all. But I have to write it for the sake of completeness. So, here comes the ubiquitous review: Harry Potter and Half Blood Prince. Will make it brief.
When the book first came out, it was meant for young adults. Now, over a period of seven years, those people must have grown up. But still, that doesn't necessisate the tone of the book to change. It will still be read by other young adults. But it, looks like JKR forgot the above equation, and wrote a book devoid of "charming" humor (puns intended!). I wonder what would have happened if Enid Blyton had done the same with Malory Towers. Harry Potter & HBP is as dark and depressing as it could be. In certain parts, its slightly too dramatic.
Storywise, its a book where she has put the premise straight, parts of stories from the previous parts are re-told. Ron, Hermione and Harry seem to behaving as adolescents. There is some inconsequential icky-wicky romance. A character is killed. Another character is killed. The book doesn't finish with the usual face-off, but goes into a lot of detail about what happened in the past. In short, all the loose strings are tied up, and the stage is set for the seventh part.
It will be a long wait!