"Marvel's Iron Man 3" Tony Stark/Iron Man (Robert Downey Jr.). (Zade Rosenthal)

In his recent keynote address at the San Francisco International Film Festival, during which he consigned most of modern filmmaking to a dust-heap of once-shiny detritus and disposable trash, Steven Soderbergh made a keenly observed distinction between movies and cinema, noting that “a movie is something you see, and cinema is something that’s made.”

It’s difficult to see how that pithily elegant rubric might accommodate “Iron Man 3,” which seems designed less as an artisanal object or visual entertainment than a full-body assault on the senses.

A frantic, occasionally funny, finally enervating bricolage of special effects, explosive set pieces, sardonic one-liners and notional human emotions, this branch of the Marvel franchise tree feels brittle and over-extended enough to snap off entirely. From its anxious protagonist and the battered metal sheaths he dons to save the world to the clattering, fiery mayhem that ensues with metronomic predictability, “Iron Man 3” is less a movie than a final war whoop let loose before utter exhaustion sets in.

Which isn’t to say that this installment doesn’t have its moments. Taking the reins from series director Jon Favreau, Shane Black has enlisted a fine ensemble to bring a beloved chapter of Tony Stark’s saga to life, including a crafty Ben Kingsley as villain-du-jour the Mandarin. After a prologue in which Tony meets scientists Maya Hansen (Rebecca Hall) and Aldrich Killian (Guy Pearce) in Switzerland, the story catches up with our playboy-inventor-superhero in the present day, shortly after he has lit up New York with the rest of his Marvel brothers in “The Avengers.” Plagued by his brush with death, Tony can’t sleep, and nearly every encounter with a fan or mention of “New York” sends him into paroxysms of anxiety. Having met Norse gods and touched the Big Nothing, he worries, “I’m just a man in a can.”

Robert Downey Jr. plays the existential angst the way he plays all of Tony’s feelings in “Iron Man 3,” with a glib, whip-crack off-handedness that would have been at home in a 1940s screwball comedy, and that has helped levitate the “Iron Man” series from being a mere exercise in CGI bombast and macho over-compensation. His banter with computer-valet Jarvis (delightfully voiced by Paul Bettany), as well as with body man Happy Hogan (Favreau), love interest Pepper Potts (Gwyneth Paltrow) and the various fans he encounters on his travels accounts for most of the laughs in “Iron Man 3,” which will take Tony from his post-modern Malibu aerie to Tennessee and Florida.

Some of the picture’s best moments transpire between Tony and a young boy named Harley (Ty Simpkins), who helps his hero with a digital Dora watch and some spare parts from his potato gun.

One of the big draws of “Iron Man 3” is seeing how Tony will deploy the band of “brobots” he has been building in his workshop in Malibu. He and his cohorts — including Col. James Rhodes (Don Cheadle) — slip in and out of so many aerodynamic sarcophagi that “Iron Man 3” begins to take on the contours of “Attack of the Clones” (with all the unfortunate associations such a comparison suggests).

After a frenetic attack on Tony’s Malibu dream house, the decimation of downtown Los Angeles by a pack of molten-skinned bad guys and a daring mid-air rescue, there’s nowhere to go but bigger and louder. The great danger of “Iron Man” has always been that it winds up looking and sounding like “Transformers,” as those metallic body-pods hurl themselves at Tony with punishing ballistic force. This iteration is no different, even though it’s not just Tony who turns into a knight in clanking, occasionally malfunctioning, armor.

The occasional twists notwithstanding, “Iron Man 3” doesn’t pack much by way of surprise or invention. Presumably it will still satisfy what the audience has come to expect from the series (“Iron Man 3” already has cleared $240 million overseas). But, especially after the bright, lively “Avengers” last summer, it feels murky and draggy, all the more so for 3-D photography that saps its crowded, busy images of dynamic range.

At one point, Tony presents Pepper with a Christmas gift of a huge, goofy, overstuffed rabbit — a seemingly obvious Trojan Bunny that winds up having no narrative function whatsoever. Sometimes a huge, goofy, overstuffed rabbit is just a huge, goofy, overstuffed rabbit — and even a huge, goofy, overstuffed rabbit can get a little threadbare.

“Iron Man 3” ends with a tone of finality which, even if it’s ersatz, feels like a well-earned respite. It seems only fair to let the man in the can rest in peace, at least for now.

PG-13. At area theaters. Contains sequences of intense sci-fi action and violence throughout, and for brief suggestive content. 129 minutes.