The sixth book in the series sees Harry really become Dumbledore's protegé. Dumbledore has clearly decided that Harry is no longer a boy and is now a man (or close enough) and starts to tell him more than he has previously. He tells him about Tom Riddle as a boy and passes on all the information he can to help him in the inevitable quest (AKA the giant elephant in the room) and starts to take him out of school on trips. Harry is also shown more of Dumbledore's memories of Tom as a child who in turn becomes more human. As the book continues, different elements of his youth are uncovered and really help Harry to better understand his nemesis. He also explains that parts of Voldemort's soul are hidden in objects and they start their search to destroy them.
Harry must also spend a lot of his free time (which is just eaten up by all his extra-curricular activities!) hanging out with his favourite teacher - Snape. Snape has been assigned the fun task of teaching Harry how to keep Voldemort out of his head, something that is now becoming far more than just the odd vision and dangerous.
Meanwhile, in the classroom Harry manages to get his hands on a ridiculously old and shabby looking text book in his potions class which he soon learns is a blessing in disguise as it has very helpful notes in the margins. Of course, Hermione morally objects and Ron just wants to copy. But the mystery remains - who does the book belong to? Who is the Half-Blood Prince?
With the book, Harry manages to go straight to the top of the class, greatly impressing new teacher Professor Slughorn - a teacher who is quite proud of his list of promising and well connected students he has taught over the years. Dumbledore gets Harry to befriend him in order to uncover a memory Slughorn is so ashamed of that he has even warped it in his own mind... but what could he be hiding? What did he tell his star pupil Tom Riddle all those years ago...?
Book 6 is made great by one of the most dramatic cliffhanger endings in the entire series. The biggest shock awaits the reader as one of the major characters is killed off and the book is left hanging, not knowing what is going to happen next...
The film was largely a good conversion and focused so much on the genius of Alan Rickman as Snape that you forgot that hardly anybody else gets much screen time. HBP also sees the introduction of the brilliantly weird and oddly cuddly Jim Broadbent as Prof Slughorn who pulls off the role perfectly. He manages to be the perfectly flawed character that JK Rowling created, who has been led astray by the glory of fame and success as so many good and decent people have been.
One of Dumbledore and Harry's trips is also fantastically dark and done so well that the end result is chilling and gripping throughout as dark, scary creatures come out of the water and after the pair. It also sees the transition as student becomes the equal to his teacher.
Then you get to the ending which was changed unnecessarily and greatly angered me. I have said before that I don't mind changes when they make sense but this one doesn't. The death scene in the book sees Harry thrown against a wall against his will, silenced with magic and covered with his invisibility cloak. He cannot move a muscle and cannot speak but he must witness the scene as it unfolds. The horror of that was gripping and you really felt him trying to leap out of his invisible prison to save the day. In the film, they had him hide out of sight. The Harry Potter we all know and love would not have stood by and done nothing, no matter what the danger to himself, unless he absolutely had no choice. It just didn't make sense and made the entire scene much less shocking. The frustrating part though is that it saved nothing in time and would possibly have worked even better on the big screen than in the book. The said death just didn't get the drama it needed.
That said, the final scene immediately after it did tug at the heart strings and was a very moving and fitting tribute.
Check out Harry Potter 7: The Deathly Hallows - Part 1 and Part 2