These Hogwarts kids are growing up quick.

The first thing a viewer notices is how Harry Potter’s voice has changed. In addition to the deeper tone, actor Daniel Radcliffe has a wiser and more confident demeanor ?” no doubt stemming from the personal experience of going from complete anonymity to international fame during the past year.

Harry’s best friend Ron Weasley (Rupert Grint) also has been visited by the puberty wizard, with an adult voice to go along with his two facial expressions: worried and more worried.

Adding to this hormonal foot race is arch rival Draco Malfoy (Tom Felton), who’s grown from a pip-squeak to being a foot taller than Harry.

Like the cast, the film franchise itself is maturing.

The sequel to 2001’s astronomically popular “Harry Potter and the Sorcerer’s Stone” is a much darker, more intense picture than its predecessor. The characters appear less apprehensive about their roles within this adored pantheon, as does director Chris Columbus, who displays superior mechanical skills.

Yet “Chamber of Secrets” is not quite the magical mystery tour that the first one was. Despite some major improvements, the movie is often sluggish in pacing and intrigue.

Don’t fault author J.K. Rowling, whose follow-up novel was arguably more entertaining than her first. “Chamber of Secrets” concerns Harry’s sophomore year at Hogwarts School of Witchcraft and Wizardry, where secrets from the institution’s past begin to plague the hero. With help from his best friends Ron and Hermione (Emma Watson), Harry tries to piece together clues involving an arcane diary and figure out the source of a serpentine whisper that only he can perceive.

Daniel Radcliffe reprises his title role as a novice wizard in Harry

“Even in the wizarding world, hearing voices isn’t a good sign,” Hermione tells him.

Before long, Harry is battling the sinister forces of Slytherin that have made Hogwarts a target.

There are several ways this sequel surpasses the original, with the most dramatic difference being the special effects. From a floating car to an enraged tree known as a Whomping Willow to a rousing Quidditch match (a breakneck sport played on flying broomsticks), the sequences seem crisp and convincing.

Particularly impressive is that of the purely computer-generated Dobby, a house elf who warns Harry that a fiendish plot is developing. With expressive green eyes, a pointy nose and tattered clothes, Dobby is a marvel of animation. He is probably what “Star Wars” creator George Lucas envisioned Jar Jar Binks as being ?” but was unable to accomplish ?” when he attempted to seamlessly blend a digital character with live action.

Also very good is a terrifying foray into the forbidden forest, where giant spiders try to make Harry and Ron their meal. This is one squirm-inducing sequence, filled with creatures as menacing as those from “Eight Legged Freaks.”

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In fact, much of the film is appreciably more ominous. (Will pre-teens have nightmares after sitting through this stuff?) It doesn’t seem like an artistic choice on the part of filmmaker Columbus, rather it’s just an equally faithful adaptation of the book, which itself was darker than the first installment.

Unfortunately, the tone may be more creepy, but it is NOT more exciting.

“Chamber of Secrets” bogs down during its middle portions. Secondary characters are introduced (Kenneth Branagh as a prima donna prestidigitator, Bonnie Wright as the youngest Weasley) that have a presence either too minor or too major in relation to how the mystery resolves. Only the infallible Jason Isaacs (the villain in “The Patriot”) makes much of an impression as the rich and abusive patriarch Lucius Malfoy.

There is arguably more exposition in “Chamber” than in “Sorcerer’s Stone,” which is quite unusual for a sequel. In the first movie, Harry was gradually introduced to the covert world of sorcery, and viewers got to share in his education.

Plot points unfold rather clunkily in “Chamber,” with scenes of verbal exposition overflowing like bubbling cauldrons. This explains why the running time is nearly three hours, because otherwise there wouldn’t be enough room for so many lengthy monologues that spell out what’s going on.

Few fans of the books complained that the initial film was two and a half hours long. If anything, they wanted more of Potter, because they couldn’t stand the idea that anything was being omitted from Rowling’s classics.

With “Chamber of Secrets,” they’ll get more: more characters, more visual effects, more terror, more action.

Oddly enough, they won’t get more entertainment.