The consensus about Harry Potter and the Half-Blood Prince is that it was a pretty good movie, but would have made a better TV series. I’ve been saying the same thing since The Goblet of Fire, and really about most novels that are made in to movies. and this isn’t even fannish griping about my favorite little moment being left out for plot expediency. Most novels are twenty gallon stories wearing a ten gallon hat. HBP was more relaxed and had some of the character moments that were lacking in the last two films, but still suffered from an excess of plot. But that is part of the problem with cramming a 650 page novel into two and half hours of movie. You have to break your neck swinging form one emotional arc to the next, just to fit everything into the allotted time.
Now, as a series, you have between 13 and 20 episodes to dwell on the character moments that make the story come alive, while still handling the various plots and subplots in a way that allows for subtly, drama and levity. You can spend a whole episode dealing with the Ron-Lavender-Hermione love triangle, as a break from emo Malfoy and the cabinet of doom, the whole business with Harry and the spell book, and the larger political fight going on as the buildup to the war escalates. Alternate this with prolonged episodes of Harry and Dumbledore in the Pensieve, hunting for horacrux and playing quidditch and you’ve got a pretty full season of television, right there. Squeezing all that into a movie leaves you wandering what’s happening, unless you’ve already read the books. Which just makes the movies little more than a visual plot summary rather than a living, breathing story on film.