Five films in, the Potter films had moved beyond being merely 'established' and were now regular fixtures in the movie calendar. Predecessor Order of the Phoenix had the highest box office since the first, and the Potter team kept the faith with director David Yates for Harry Potter and the Half-Blood Prince.
The big new acting name was Jim Broadbent as Horace Slughorn, a retired Hogwarts potions master teased back into his old job by Dumbledore. After the relative high-jinks of the first two films, the air of darkness which started to envelop proceedings over the previous three films became deliciously suffocating here, though it was also punctuated by some very sharp stabs of visual humour - Cormac McLaggen's fly-catching is a personal favourite.
Of that unfortunate incident... some fans of the books were up in arms over a vital change, arguably the biggest in the series. In Rowling's piece, Potter had been put under a spell by Dumbledore to freeze him while the standoff above took place. To their credit, Kloves and Yates left that out, layering on the levels of moral complexity and questions of choice and sacrifice.
Other key changes included the fiery destruction of the Weasley Burrow and the opening scenes where Death Eaters take on London's Millennium Bridge. "I just thought it'd be really cool to see that, again, just to make the audience feel what the Death Eaters are doing to the Muggle world," Yates explained at the time.
While The Guardian's Peter Bradshaw criticised the movie for being "more hormonal, more teenage-angsty and sadly more boring", The Times' Kevin Maher marked it out as the best in the series. It failed to win an Oscar, but the nod for Bruno Delbonnel's cinematography was arguably the most serious recognition the films had yet received from the Academy.
By the release of Half-Blood Prince, it as well-known that the final 600+ page Deathly Hallows would be split into two films, and that Yates would be directing them back to back. With a bitter, cliffhanger ending, things were teed up perfectly.
More Harry Potter retrospectives:
> 'Harry Potter and the Philosopher's Stone'
> 'Harry Potter and the Chamber of Secrets'
> 'Harry Potter and the Prisoner of Azkaban'
> 'Harry Potter and the Goblet of Fire'
> 'Harry Potter and the Order of the Phoenix'
Move through our Harry Potter and the Half-Blood Prince gallery below: