J.K. Rowling’s powerful writing revels in the wonderment of everything — the first stirrings of true love all the way to fantastic depictions of fictitious wizardry. Although Rowling’s later Harry Potter tales can get bogged down in detail, they never lose that sense of fascination — which was the very focal point of their success.

How stupefying and sad, then, that the Harry Potter films have chosen bloat over beguilement and adherence to realism that stifles Rowling’s trickster-storytelling wiles.

Harry Potter and the Half-Blood Prince is the second film in the franchise directed by David Yates, and his stamp bodes poorly for the story’s final moments. (He’s also directing the two-part cinematic split of Harry Potter and the Deathly Hallows.)

All but a handful of moments in Half-Blood Prince feel like a loop back around to the laziest parts of Yates’ take on Harry Potter and the Order of the Phoenix. And this time, there’s not even a villain as buoyant as Dolores Umbridge to shake off lethargy.

Yates’ direction does work in fits and starts, namely the careful touch he brings to the very opening shot — Professor Albus Dumbledore’s (Michael Gambon) steady, guiding hand on the uneasy, quivering shoulder of Harry Potter (Daniel Radcliffe).

Mortally entwined with the evil Lord Voldemort (Ralph Fiennes, sorely missed in this installment), Harry has seen so many spells cast in the name of destructive evil.

Looking forward to a mental escape from his torment in his latest year at Hogwarts, Harry instead finds a potions-class text belonging to the “Half-Blood Prince” — a book that guides him effortlessly through even the most challenging concoctions.

Soon enough, he and his best friends — Ron (Rupert Grint) and Hermione (Emma Watson) — are pulled back into Voldemort’s vicious cycle of violence.

His minions (led by Helena Bonham Carter) wreak havoc in plain daylight on humans in London. Dumbledore exposes Harry to extracted memories of one Tom Riddle (Hero Fiennes-Tiffin, Ralph’s nephew). And Professor Horace Slughorn (Jim Broadbent, a sort of Milton Waddams for the Harry Potter universe) — who takes Harry as a prized pupil — may be connected to the dark lord.

As teen romance is concerned, Half-Blood is hormonal without getting horndog, although plenty wily within the confines of its PG rating. But a squidgy middle section with everyone going lulu over each other loses luster, and glossing over cliquish developments among Harry, Ron and Hermione turns things tepid. Harry Potter and the Goblet of Fire remains the only film in the franchise to reconcile the teens’ romantic longings with the ornate fantasy storytelling.

Just when they should be at their peak, the stakes feel small (namely in a clumsily filmed wheat-field chase). And right as the tale should take on titanic weight, it turns turgid. Without spoiling anything, Yates botches what should be the emotional highpoint of the saga thus far, choosing to film it from a purely passive perspective.

He also relegates the identity of the Half-Blood Prince to an afterthought — an “oh, um, yeah, sure” moment meant to explain the title in a quick rush toward the finale.

There is joy to be found in Half-Blood, just as there has been in all of the movies — watching Radcliffe, Grint and Watson grow as characters and performers.

Radcliffe conveys understated, square-jawed respect for the challenging things a beloved mentor must ask a student to do. Watson is quietly devastating as unrequited love unmoors Hermione from her proper behavior. And Grint walks that tricky line between Ron’s spotlight jealousy of Harry and his loyalty as a friend

These are wonderful performers, and it’s a strong hope that each has an acting future beyond this franchise. The magic is still there for them, but it has all but gone from the Harry Potter films.