I find the sixth entry in the Harry Potter franchise almost entirely forgetful. Rewatching the films has reminded me how much I still remember about the books and many of the cinematic scenes have stuck with me over the years. Not so with The Half-Blood Prince. I remember almost nothing of the film (so much I'm genuinely unsure if it is a rewatch or not), don't recall the book at all and actually just had to Google the title whilst writing this review!
I think it may have something to do with the plot feeling very much open-ended. A large part of the storyline concerns itself with setting up future plot threads or resolving lingering inconsistencies, particularly with inter-character relationships, which are focused on a lot. I can fully understand if the emphasis on teenage romance is why The Half-Blood Prince feels so lacklustre, but I think the film almost amplifies the effect. The titular mystery doesn't so much take a backseat in the film as it is almost entirely ignored. The textbook that introduces the character has been reduced to a simple plot device allowing Harry and Slughorn to coherently form a relationship, though simultaneously is undercut by Dumbledore's belief that being the "boy who lived" is reason enough for Slughorn to desire Harry's entry to the collection of students he prizes so much.
As a result, the end revelation regarding the identity of the Half-Blood Prince, the subsequent betrayal of Dumbledore and the (seeming) conclusion to the whole Snape question feels somewhat lacking. The book is arguably the one entry in the series which focuses on a character other than Potter and Voldemort: Severus Snape himself. The relative lack of the occlumency lessons and, particularly, the insights into Snape that they reveal means that the character remains far more mysterious and open to interpretation in the film. Instead, the emotional impact has been shifted onto a "will they, won't they" circus of teenage angst surrounding Harry, Ginny, Ron and Hermione. Ultimately, I feel they cut the wrong plotline.
Still, the tone of the movie is well placed, with some nice colour manipulation throughout that give the film a real sense of foreboding. This isn't the work of a master producer, but it's still nice to see and lends itself particularly well to Draco's subplot. Indeed, arguably the best-crafted sequences in the film are the frequent panning shots or subtle framing used to constantly remind the viewer about Draco. Without spending too much time with the character centre stage, the crew keep us in permanent suspense as to what his plans are whilst making it clear that he is being manipulated beyond his will, isolated from his friends and family. Subtle but poignant, it's a shame the same level of care wasn't taken with the similar issues playing out between Snape and Dumbledore themselves.