
The script actually does a good job editing the book all in all, but the PG rating makes the complexity of the tale and the dread of who's on what side watered down and a minimal part of the film. As Charley states, the eponymous character - the Half Blood Prince, is more or less ignored in the film. It is pushed aside to a mere fleeting question until the film's end, when it is as tidily answered as it is posed.
Of course, Yates can put together a beautiful image. The film visually exudes the unease of the times, the ominous threat surrounds near every shot, just as it does the characters within the story. However the tone does not remain so consistent. Instead, it jumps from dark and treacherous (or an attempt at such) to humorously teenage fluff. Don't get me wrong, both are huge parts of the book, and deserve equal respect in the cinematic version.

While amusingly light-hearted and enjoyable (to a certain degree), the focus on lifting the mood through bumbling love potions and poorly hidden affections hinders the drama of the central story at hand. The climactic scenes between Harry and Headmaster Dumbledore are handled so quickly and simply that I, perhaps the most quick to cry in a theater, didn't even get misty. Life-changing moments, character-defining events, are not given the proper pace, tone, or direction. They suffer so we can all giggle at the plentiful awkward sexual innuendoes.

I think my perspective suffered from having just re-read the book, completing it a mere few hours before going to the theater. Perhaps too immersed in comparison the first time around, I look forward to giving it a second try once the finite details of the text have evaporated from my memory.
David Yates' latest addition to the Potter series is, I will agree, a good platform for the final book and films from which to spring board off into hopefully more fearless drama and PG-13 violence, like Alfonso Cuaron's Prisoner of Azkaban or Yates' Order of the Phoenix. What makes #3 and #5 better than #6? They aren't afriad to stand alone as good films, separate from the series that made them popular. #6 is good, but more than a good film in and of itself, it's just a good base for The Deathly Hallows. And a good base does not a great film make.