Again, no spoilers below, just general complaints regarding Half-Blood Prince.
I didn't think it could get worse than Chris Columbus' mangling of Chamber of Secrets. The over-long shots, the inability to cut out anything, and the absolute devotion to the mood of childlike glee were some of Columbus' worst infractions.
In HBP, Yates has some similar problems. He has created a mood of tension, of waiting, of lurking in the background, a mood that, ultimately would have been more appropriate to Order of the Phoenix, before Voldemort's rebirth is confirmed by the fight at the ministry. The mood of HBP should be more embedded with fear, with anger, with darkness. Nonetheless, Yates has created his mood, and he's sticking to it. Even the scary moments aren't really scary, just ... looming.
We all know that HBP the book is a lot of exposition, a lot of flashbacks, and not a lot of action until the last 100 or so pages, but Yates manages to excise the little action the book does have and substitute his own. He's either leaving out major scenes altogether, or simply sucking the drama out of dramatic moments, much as Columbus does, through overlong shots and a complete lack of action or acting on the parts of the leads.
Granted, some of the blame here might fall to Steve Kloves, who has made up entire scenes out of nowhere. Ginny is suddenly much more involved, and her involvement changes the course of the plot several times. Most of the interjected scenes do not majorly affect the main themes of the book, but for those of us who read it, are distracting nonetheless.
What does affect the main themes of the book is the lack of the one significant plot thread of the book -- the memories. Although Harry experiences some of the memories, most of them are notably missing. And perhaps this is why the necessary fear is missing. We don't see a young, psychopathic Tom Riddle gradually growing older. We don't know the story of his parents, or his family, or understand the hate and superiority he feels. Lord Voldemort, stripped of these, is still scary, sure, but he's scary as any other movie villian with an insufficient backstory is scary -- he strikes fear into our hearts, but not into our minds.
I could go on, I suppose, nitpicking here and there about specific scenes, but I would find it hard to do without spoiling, so I'll leave it for now.