How much of a geek are you?

All those who confess to Spider-Man fanaticism, raise your right hand. Now bend the two middle fingers toward your palm, flick your wrist outward and shoot flying-arachnid goop on any available skyscraper. Swing to the roof of the nearest multiplex.

If you are ill-equipped for such a maneuver, do not attempt it. More pedestrian approaches to Spider-Man 3 will get you there, too, although nongeeks should enter with care. Movie goers not absorbed by the spring-wound Spidey mythos might find the running time exhausting, the subplots excessive and the mood shifts bizarre, but hard-core fans should be giddy little web-slingers. And that's not even counting the Bruce Campbell cameo.

The third Spider-Man, like the first two, was directed by genre king Sam Raimi and stars the charismatically ordinary Tobey Maguire as a young man with a radioactive spider bite. The joy of the first film was one of discovery -- look, a comic-book hero can be a nasally dork and still kick butt! -- while the joy of the second lay in its rich character byplay and oddball comic riffs.

The oddball element remains in Spider-Man 3, but the script is busy with so many supporting characters and plot detours that the series' charming idiosyncrasy is sometimes lost in the noise. Fortunately, it's entertaining noise, switching in timbre from giddy innocence to swivel-hipped ironic cockiness to fanged vengeance and back again, often in the space of a few tidy scenes. The name of the game is sudden, turnabout character change: Good guys go bad, bad guys go good, and M.J. nearly goes off the deep end with frustration.

You'll recall M.J. as Spider-Man's main squeeze, ably rendered by the melancholic Kirsten Dunst. As the movie begins she's starring on Broadway and crazy in love with Spidey's quotidian alter ego, Peter Parker. He plans to pop the question, but there are hitches, including a venomous rival photographer (Topher Grace, bleached hair signaling dubious moral rectitude), an escaped convict turned Sandman (Thomas Haden Church) and a still-ticked-off Harry Osborn (James Franco, back for thirds) seeking to avenge the death of his pa, the Green Goblin.

Peter also has to cope with his own inflated head: "People really like me!" he crows in a Sally Field moment of bubbleheaded swagger. But his main problem is a cosmic black ooze that binds to his cellular structure, knits him a black Bad-Spidey costume and makes him an angry, angry boy. It also makes him look like the bassist for an emo band: Is that Pete Wentz behind the bangs? Spider-Man's trip to the dark side is played half for laughs, half for the benefit of free-will philosophizing ("We always have a choice") that cuts to the heart of every comic book.

Spider-Man 3 is funny here and touching there, but it's also relentlessly violent -- and utterly inappropriate for small children. The action bits are cartoonish and unrealistic, yes, but watching a man's head get ground to dust on the side of a speeding subway car is not the stuff of nursery rhymes. Other sequences are magically imaginative, especially Church's sculpted transmutation -- thank you, particle physics lab -- from brokenhearted convict into monstrous Sandman.

Fans love ranking franchise installments (Empire, then Star Wars, then Jedi), so I'll save them some work: Spider-Man 2 is the best of the lot, then Spider-Man 3, then Spider-Man 1. Feel differently? E-mail me. Extend right index finger, bend at knuckle, click "send."

amy.biancolli@chron.com