SPOILER WARNING: The following contains spoilers for "Harry Potter and the Half-Blood Prince."
Opening today in the U.S., "Harry Potter and the Half-Blood Prince" wonderfully conveys the miasma of puberty, but is ultimately unrewarding... as our hero fails to grow up.
The film begins with flashes that call back to the previous installment, "Harry Potter and the Order of the Phoenix." The villainous wizard Lucius Malfoy (Jason Issacs) is imprisoned, while a bloodied Harry Potter (Daniel Radcliffe) is photographed, then led away by his mentor Albius Dumbledore (Michael Gambon). Although these flashes are too brief to bring new viewers completely up to speed, they succeed in establishing Harry and Malfoy's son Draco (Tom Felton). Harry is a celebrity, allegedly the "chosen one" -- a wizard with the power to vanquish the evil Lord Voldemort. His counterpart Draco is destined for a life of evil with Voldemort's "Death Eaters," regardless of his own desires.
The threat of the Death Eaters makes up one of three storylines that run throughout most of the film. On behalf of Voldemort, the Death Eaters attack the "Wizarding" world as well as that of the Muggles (non-magical folk). Hogwarts School of Witchery and Wizardry is no longer a safe haven for wizards in training, and the skies above are now a perpetual gray (actually clouded by the specter of Voldemort), providing the murky atmosphere for the film. Draco acts as a pawn in the evildoer's plan, experimenting with a mysterious "vanishing cabinet" kept at Hogwarts. Draco's plight, and the lack of control of his life symbolize the turbulence one experiences during their teenage years.
Dumbledore's preparation for the upcoming final battle with Voldemort is the second storyline of the film. In order to uncover the vital key to the Dark Lord's defenses, Harry works with Dumbledore to befriend Hogwarts' returning Potions Professor, Horace Slughorn (Jim Broadbent), and recover a memory of Slughorn's involving a former student, Tom Riddle (played in flashbacks by Hero Fiennes-Tiffin & Frank Dillane). Riddle would later become the sorcerer Voldemort. During Slughorn's potions class Harry also acquires the former textbook of "The Half-Blood Prince," a gifted student of Hogwarts from which the film (and book) takes its name.
Potions - or at least a box of love potion-laced chocolates - are an element of the third storyline, an often-humorous love triangle between Ron Weasely (Rupert Grint), Lavender Brown (Jessie Cave), and Hermione Granger (Emma Watson). Harry also has love problems of his own with Ron's sister Ginny (Bonnie Wright), but curiously Harry never suffers the same romantic torture as his friends. This unfortunately results in Harry's friends being more sympathetic and memorable than he is.
Harry and Dumbledore eventually learn the truth behind Slughorn's missing memory, and the secret of Voldemort's invulnerability, but they are unable to truly put their knowledge to use, as the Death Eater's plan reaches fruition, and they attack with the help of an apparent traitor to Hogwarts who finally reveals the identity of the Half-Blood Prince.
It's at this point - the climax - where you hope to see Harry rise to the challenge and be his own man, demonstrating his passage into adulthood through action. But rather than being an adult, Harry chooses to remain the child and follow the plan of the Machiavellian Dumbledore. Harry pays dearly for his choice as the Death Eaters subsequently kill his mentor, and we suffer along with him.
Hogwarts' student body banishes the cloud specter of Voldemort soon thereafter, but the effect isn't sufficiently uplifting. The choices in the climax serve the overall storyline of the franchise, but on its own the film feels disappointing because Harry's growth is stunted.