"Avengers: Age of Ultron" is huge in size and destined to be an enormous, record-breaking financial success, its $250-million price tag virtual pocket change next to the $1.5-billion-plus it will earn at the box office. If there is a sure thing in this world, it is this eagerly anticipated follow-up's international domination. With that said, returning writer-director Joss Whedon has a difficult time hiding how overwhelmed he is by the pressure of making something bigger and better than 2012's "Marvel's The Avengers." On this latter point, it shouldn't have been such a daunting task; as much as some viewers may have enjoyed the prior film, there was definite room for improvement in a picture that followed a decidedly by-the-numbers path and survived more or less on the novelty of seeing a wide range of Marvel superheroes joining forces onscreen for the first time. In crafting a second installment, Whedon has succumbed to the weight of this very undertaking, tossing too much muchness in front of the screen and crossing his fingers that it will stick. Some of it does, some of it doesn't, and most just comes off as forced.

When the Avengers team—that is, Tony Stark/Iron Man (Robert Downey Jr.), Steve Rogers/Captain America (Chris Evans), Thor (Chris Hemsworth), Bruce Banner/The Incredible Hulk (Mark Ruffalo), Natasha Romanoff/Black Widow (Scarlett Johansson) and Clint Barton/Hawkeye (Jeremy Renner)—narrowly retrieve Loki's powerful, much-coveted scepter from the clutches of Hydra, Tony and Bruce are surprised to discover that it harbors an artificial intelligence inside it. No sooner have they secretly built Tony's sentient global peace-keeping initiative, named Ultron (James Spader), when the advanced A.I. rebels and escapes with the scepter. Pulling two of Hydra's human experiments into his fold—vengeance-seeking twins Pietro Maximoff (Aaron Taylor-Johnson), lightning-fast, and telekinetic mind-shredder Wanda (Elizabeth Olsen)—Ultron seeks to build an army of robot drones, destroy the Avengers, and ultimately lay waste to the planet's entire human population.

Following 2014's smartly written, tautly constructed conspiracy-thriller-posing-as-a-superhero-adventure "Captain America: The Winter Soldier" and that same year's heartfelt, witty, deliciously entertaining "Guardians of the Galaxy," "Avengers: Age of Ultron" fades in their shadows like an afterthought. Despite being convoluted and lacking in some of the hows and whys, the plot, to Whedon's credit, is woven capably enough that it doesn't feel like simply a 142-minute exposition session. What it too often does feel like is a virtual replay, with only changes in location and an increase in characters to separate it from the previous entry. Title villain Ultron is well-voiced by James Spader and gets a few wickedly cool characteristics, including his recurring "I've Got No Strings" callback to Disney's 1940 animated feature "Pinocchio," but the longer he is around the more glaringly one-note he becomes.

On the multi-protagonists' side, there is something oddly stale and prefabricated about their interplay. The sly humor of "The Avengers" pushes too hard here, the cloying one-liners and asides more unctuous than easy-going and amusing. With hints of a "Beauty and the Beast" vibe (minus the charm), an out-of-nowhere romance between Natasha and Bruce is stale and unconvincing, made all the more annoying because Natasha's much more potent chemistry with Steve was already effectively established in "Captain America: The Winter Soldier." Save for one fleeting exchange, however, this far more promising relationship is tossed to the wayside. Scarlett Johansson (2014's "Under the Skin") continues to develop Natasha into one of the more complicated and interesting figures among all her cohorts, and she manages to do it without having any special powers beyond her agility and wits. As Bruce, Mark Ruffalo (2014's "Foxcatcher") has found his footing in the role and brings a softer side to his Hulk. The problems stemming from their burgeoning misbegotten love story is no fault of either actor, but of a script that pushes them together from the start when there are precious few sparks between them.

Much of the overflowing ensemble are by now capably ensconced in their respective comic-adapted personas. Chris Evans (2014's "Snowpiercer") was and continues to be impeccably cast as Steve Rogers/Captain America, though his only real chance to further explore his part is in his brief hallucinations of old flame from the 1940s Peggy Carter (Hayley Atwell). As Thor, Chris Hemsworth (2015's "Blackhat") wields his hammer with force—this turns out to be a small yet notable plot point—but otherwise gets the short end of the stick with not much of substance to do. By contrast, more is discovered about the previously enigmatic Clint Barton/Hawkeye. Despite this, the typically magnetic Jeremy Renner (2013's "American Hustle") appears bored and even a little aloof in certain scenes. The eldest and arguably most seasoned of his compatriots, Tony Stark/Iron Man has been the unofficial leader in both "Avengers" movies, which makes Robert Downey Jr.'s (2014's "Chef") lack of screen time a little surprising. He is around throughout, but isn't focused on very much and frequently tends to drift out of frame.

The most eye-catching performance comes from a newcomer to the franchise. As the mind-ripping Wanda Maximoff/Scarlet Witch, Elizabeth Olsen gets to join the action in a way she never got the chance to in Gareth Edwards' otherwise crackerjack 2014 monster movie "Godzilla." Without giving too much away, Wanda starts the film as a resident heavy, becomes a designated henchwoman to Ultron, and then goes through another change that suddenly gives her an unexpected and welcome depth of conscience. Olsen sells every metamorphosis and conflicted emotion of her character, a young woman searching for her place in a life haunted by tragedies from her past. As twin Pieter, Aaron Taylor-Johnson (who, oddly enough, played her husband in "Godzilla") is only okay, serving his purpose but not standing out. Had the bond between Pieter and Wanda been strengthened, key scenes in the third act would have carried with them greater impact. All the same, Olsen is a standout—and sells her Russian accent, to boot.

"You know I support your avenging," Clint's patient but concerned wife, Laura (Linda Cardellini), tells him without a hint of tongue-in-cheek irony before dutifully returning to raise their gaggle of children and wash the dishes. If Laura is on hand for no reason other than to reveal that Clint has a personal life outside of shooting arrows, that still doesn't make it right that she is treated so thanklessly in the grander scheme of saving the world. An inferior sequel that brings little joy to its grandiosity, "Avengers: Age of Ultron" carries the vague aroma of uninspired, box-checking functionality. There are no scenes that come close to the first film's crowd-pleasing spectacle of Loki getting Hulk-smashed or that awesome, swirling unbroken shot during the climax that observed all of the Avengers in the midst of battle. Whedon tries to emulate something similar right at the start, but the technical coolness of a comparable long-form shot is rendered clunky and ineffective because the viewer has joined the characters in medias res without yet knowing who they are fighting and why. The up-front placement of these intricate examples of empty dazzlement are, like the film itself, a miscalculation, the narrative growing in complication as the diverting but largely unmemorable action strikes progressively familiar beats. "Avengers: Age of Ultron" has a been-there-done-that aura. For the upcoming two-part "Avengers: Infinity War" films due in 2018 and 2019, the guiding motto of directors Anthony and Joe Russo (taking over for Whedon) should be precisely the opposite: whatever has been done before, do differently.