It will surely stand as one of the most peculiar and possibly ironic entries in a director’s filmography that, in between Joss Whedon’s two “Avengers” films, there reads “Much Ado About Nothing”: a low-budget, black-and-white Shakespeare adaption sandwiched between two of the most gargantuan blockbusters ever made.

In “Avengers: Age of Ultron,” Whedon (and Marvel’s) sequel to the third highest grossing film of all-time, there is definitely aplenty ado-ing. Too much, certainly, but then again, we come to the Avengers for their clown-car excess of superheros, their colorful coterie of capes.

What binds Whedon’s spectacles with his Shakespeare are the quips, which sail in iambic pentameter in one and zigzag between explosions in the others. The original 2012 “Avengers” (which featured the rarest of superhero movie insults: “mewling quim”) should have had more of them, and there’s even less room in the massive — and massively overstuffed — “Age of Ultron” for Whedon’s dry, self-referential wit.

As a sequel, “Age of Ultron” could have amped up the brio. But it instead pushes further into emotionality and complexity, adding up to a full but not particularly satisfying meal of franchise building, and leaving only a bread-crumb trail of Whedon’s banter to follow through the rubble.

The action starts predictably with the Avengers, now assembled, assaulting a remote HYDRA base in the fictional, vaguely Eastern European snowy republic of Sokovia. They are a weaving force: Robert Downey Jr.’s Iron Man, Chris Hemsworth’s Thor, Mark Ruffalo’s Hulk, Chris Evans’s Captain America, Scarlett Johansson’s Black Widow and Jeremy Renner’s Hawkeye.

Their powers are as various (supernatural, technological, mythological, lab experiments gone wrong) as their flaws (Iron Man’s narcissism, the Hulk’s rage, the Black Widow’s regrets). Downey’s glib Tony Stark/Iron Man is the lead-singer equivalent of this super group and, I suspect, the one Whedon likes writing the most for. “I’ve had a long day,” he sighs. “Eugene O’Neill long.”

What “Age of Ultron” has going for it, as such references prove, is a sense of fun, a lack of self-seriousness that persists even when things start going kablooey — something not always evident in other faux-serious superhero films. (I’m looking at you, “Man of Steel.”)

In Sokovia, they encounter the duplicitous twins Quicksilver (Aaron Taylor-Johnson) and Scarlet Witch (Elizabeth Olsen). She can, with a crimson-colored magic, read minds, and he’s lightning quick. They, however, aren’t the movie’s real villains: That’s the titular Ultron, an artificial intelligence that the Scarlet Witch slyly leads Stark to create, birthing not the global protection system he hopes, but a maniacal Frankenstein born, thankfully, with some of his creator’s drollness.

Ultron (James Spader) builds himself a muscular metallic body and with the supposed cause of world peace, begins amassing a robot army to rid the planet of human (and Avenger) life. Spader plays Ultron too similar to other mechanical monsters to equal Tom Hiddleston’s great Loki, the nemesis of the last “Avengers” film. But Spader’s jocular menace adds plenty. He wickedly hums Pinocchio melodies: “There are no strings on me.”

But the drama of “Age of Ultron” lies only partly in the battle with Ultron, which skips around the globe, to Seoul and South Africa, due to only slightly logical pursuits of rare metals and a tissue-generating invention. The film is really focused on the fraying dysfunction of the Avengers and their existential quandaries as proficient killers now untethered from the dismantled S.H.I.E.L.D. agency.

Most successful are the tender scenes between Ruffalo’s Bruce Banner/Hulk and Johansson’s former Russian spy. She’s something like his LSD trip guide, soothing Ruffalo’s enraged “big guy” with her soft voice, petting his hand until he shrinks back to Banner and the green dissipates.

There’s not a wrong note in the cast; just about anything with the likes of Spader, Ruffalo, Johansson, Hemsworth and Downey can’t help but entertain. But the dive into the vulnerability of the Avengers doesn’t add much depth (is the home life of an arrow slinger named Hawkeye important?) and saps the film’s zip.

All the character arcs — the Avengers, the bad guys and the new characters — are simply too much to tackle, even for a master juggler like Whedon. Paul Bettany, previously the voice of Iron Man’s computer, J.A.R.V.I.S., arrives late as the Vision, a preternaturally poised floating hero resembling a red Powder.

The movie’s hefty machinery — the action sequences, the sequel baiting — suck up much of the movie’s oxygen, and the mammoth action scenes have a way of crushing the smaller moments. Better is when the Avengers are just sitting around, musing about the physics governing Thor’s heavy hammer.

In the relentless march forward of the Marvel juggernaut (the next “Avengers” movies are slated for 2018 and 2019), “Age of Ultron” feels like a movie trying to stay light on its feet but gets swallowed up by a larger power: The Franchise.