Martyn says HARRY POTTER AND THE HALF BLOOD PRINCE is a stop gap for bigger things, but that's not necessarily a bad thing
Its easy to knock a series of big budget films targeting children as its main audience; and its even easier to knock the mass popularity of JK Rowlings wizards-at-private-school mythology. Theres a whole raft of reasons why Harry Potter is a phenomenon of the book and film world. Arriving in the middle of summer blockbuster season is Harry Potter and the Half-Blood Prince, the sixth instalment of the gigantic cash cow. With New Line Cinema and Chris Weitz ruining Philip Pullmans The Golden Compass, Harry Potter still has no competition in the childrens fantasy-drama genre. Many have tried and all have failed. The character is a pop culture icon with no peers. 
It was a smart move by the producer David Heyman to stop hiring different directors for each film and get somebody to see the series to the finishing line. Step forward, David Yates whose The Order of the Phoenix ventured into more adult, well, teenage territory. That the director of television dramas such as Sex Traffic and State of Play is responsible for what will have been four episodes in the epic adventure (The Deathly Hallows is being split into two parts) is a remarkable achievement/gamble for someone untested in big budget filmmaking. And lets face it, it doesnt get any bigger a gig than making Harry Potter films. Yates is a success because hes brought a greater sense of drama and subtly that was much needed. 
Harry Potter and The Half-Blood Prince picks up a few weeks after the events of The Order of the Phoenix. Harry and his classmates return for another year at Hogwarts suffering love trials as much as blood trials. It gives ample screen time to following the affairs of the heart and the longings of Harry, Hermione and Ron. After some initial and salient plot points are taken care of, the first half of the film plays like a light-hearted teen comedy. And funny it is too. The cast all excel in their roles, as frustrations and ill-timing thwart their chances of love. It could have been titled Harry Potter and The Raging Teenage Hormones. Yates has finally managed what the other directors failed to do (to various degrees): and that is for the young cast to start acting and not simply deliver their lines. Part of it comes down to the fact the cast were very young and with a great weight thrust upon them when it all began. Some are simply better than others. Yates is coaxing nuanced performances from his teenage cast. For the past couple of films at least, the trio in particular, seem very comfortable with the emotional demands of their characters and the films. Daniel Radcliffe is beginning to shine as an actor, one scene early on recalling his naughty, impish turn in Ricky Gervais sitcom Extras. Another comic strength is the addition of Jim Broadbent as Professor Slughorn - responsible for a good majority of the laughs. The downside to it all is theres a lot happening plot-wise, and lack of heart-quickening, thrill ride set-pieces. It does, however, deliver on drama and revelations. 
With much to cram into two and a half hours, it seems all over the place at times. Characters pop up and disappear: David Thewlis Professor Lupin; Robbie Coltranes giant groundskeeper Haggrid and Helena Bonham-Carters evil and electrifying Bellatrix Lastrange are reduced to cameos. Even Ralph Fiennes appears as Voldemort in a solitary blink-and-youll-miss-it flash. As with all penultimate chapters, the focus is on bridging narrative strands that will come together for the finale. Steve Kloves had the unenviable task of writing a screenplay that needs to set up events for The Deathly Hallows alongside character development; a variety of subplots; flashbacks exploring Voldemorts childhood and the pivotal mystery of the Half-Blood Prince. Its a film with a lot on its plate. The film delivers on special effects, stunning at times, and the cinematography by Bruno Delbonnel is dripping in moody, gothic atmosphere. The denouement ensures too the boy wizards darkest hour has arrived: the maelstrom that is Voldemort is raging to such an extent its looking a little grim for Harry and his friends. The film finishes with a brilliant sense of foreboding and challenge. David Yates direction has given the series a new sense of purpose. Harry Potter and the Half-Blood Prince begins full of humour and spark and gets progressively darker and sinister. Schools out for Harry Potter, but its not over quite yet.