There is no shortage of superheroic feats on display in "Avengers: Age of Ultron" performed by each and every one of the colorful -- and large -- cast of Marvel icons assembled for the sequel to the most successful comic book adaptation of all-time. But the most impressive display of strength, fortitude and good intent comes not from the costumed characters, but from writer/director Joss Whedon.

With this many characters to juggle, with story elements from Marvel Cinematic Universe films both past and pending to be picked up or put in play, and with audience expectations hovering at a higher altitude than any S.H.I.E.L.D. helicarrier could reach, to call the impossible tasks for Whedon to pull off plentiful would be an understatement. But somehow, even with more than a few missteps and setbacks along the way, the filmmaker manages to power through the many challenges along the way as steadfastly as any Avenger and ultimately winds up victorious, if a little battle-worn, at the end of the day.

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On the downside, the sequel lacks storytelling elegance of the first film, feels a tad over-packed with both characters to serve and action set pieces to amp up, features a few too many CGI effects of questionable quality and falls a little short on some of the film's B-stories -- most notably the romantic subplot involving the team's seemingly most vulnerable but probably most capable member Black Widow (Scarlett Johansson, adding welcome new nuances to the role) and the outwardly powerful but inwardly haunted Hulk/Bruce Banner (the always on-point Mark Ruffalo, walking an increasingly thin-edged line between hope and fatalism) -- but still, none of these issues come close to sinking the film.

In fact, Whedon's entertaining determination to pull off his Herculean (Thor-ian?) feats and deliver a film that ups the ante on the first and stays remarkably true in spirit to the original Marvel Comics style -- buoyed by his own celebrated knack for potent, character-revealing dialogue and witty repartee -- always keeps the movie alive and moving forward at an involving pace. You probably won't quite feel as fully emotionally engaged as you felt during "The Avengers," but you'll almost always be having as much pure fun.

Central among the films many gems is the vocal and motion-capture performance of James Spader as the central villain Ultron, who begins life as the Science Bros. brainchild of Tony Stark (the MCU's literal and figurative Iron Man, Robert Downey, Jr., as perfectly cocky and fascinatingly vulnerable as ever) and Banner, an idealistic but misguided attempt at creating the ultimate peacekeeping programming, using the power of the recently recovered scepter of Loki -- AKA an Infinity Stone, the Avengers soon learn -- as a shortcut. But Ultron's evolutionary ambitions and Oedipal inclinations swiftly turn him into a world-menacing monstrosity (and one of the more involving of the MCU menaces) and, though the character may have benefitted from just a bit more development, in Spader's capable hands -- and cold but quirky voice -- Ultron becomes the deadliest and squirreliest A.I. adversary since "2001's" HAL and "Blade Runner's" Roy Baty.

Even as Whedon adroitly employs the big guns from the solo film franchises in practically pitch-perfect ways -- Thor (Chris Hemsworth) and Captain America (Chris Evans) definitely seem to have walked directly and fully in from their recent adventures, though there are some minor disconnects between the ready-to-retire Tony Stark last seen in "Iron Man 3" and the full-throttle adventurer here). And the filmmaker wisely lavish attention on the other established team members Black Widow, Hulk and especially the oft-underserved Hawkeye (Jeremy Renner, really finding a good grove in the role), who gets many of the film's best lines and a lion's share of backstory reveals: each one of these characters come out of "Age of Ultron" worthy -- and almost demanding -- of their own sequel or prequel film.

The on-screen chemistry never quite fully clicks, however, in the attempt to build romantic bridges between Natasha and Bruce -- a few moments come close to convincing, but the vibe never feels deeper than two friends flirting and maybe hoping they feel more for each other than they do.

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Whedon also deftly finds effective places to slip in a host of familiar faces from around the established MCU -- most enjoyably, Don Cheadle's War Machine and, of course, the founding father of the Marvel Universe, Stan Lee -- in fun and rewarding ways that echo the precise way Lee, Jack Kirby, Steve Ditko and the original Marvel Bullpen built the original cohesive comic book universe 50 years ago: with wit and style. And the movie works well in putting some new pieces on the chessboard that will pay off in films to come, such as the introduction of the vibranium-rich (that's the hard-to-wreck alloy Cap's S.H.I.E.L.D. is made of, remember) African nation of Wakanda and the weapons profiteer Ulysses Klaw (a delightfully unsavory Andy Serkis). Some of this stuff is fan service, to be sure, but it also goes far in making the on-screen MCU feel increasingly expansive yet connected.

Less effective, however, is the handling of three key new characters, the mind-warping Scarlet Witch and her supersonic twin Quicksilver (Elizabeth Olsen and Aaron Taylor-Johnson, both visually striking but both employing generic Eastern European accents that ring a little too "moose-and-squirrel"-esque) and The Vision (a spot-on Paul Bettany, transitioning, via story-driven circumstances, from his role as Tony's stuffy in-suit A.I., J.A.R.V.I.S.), the fabled synthezoid hero from the comics who for many years was a signature member of the team.

There's been a lot of speculation as to what the film will take the origins of the twins, whose comic book mutant-hood is pre-empted onscreen by 20th Century Fox's current cinematic stewardship of the "X-Men" franchise. Let's say, spoiler-free, that the answers is apparently a whole lot more simple than some fans are imagining -- and a whole lot less interesting, as well. Though the siblings' involvement is the Avengers' affairs is reasonably motivated and their powers serve the plot machinations while looking good on-screen, the characters simply don't have enough room in the story to emerge fully formed -- they border on being ciphers, but Whedon imbues them with just enough importance to keep them from being lost in the crowd, if not exactly the fleshed-out Wanda and Pietro longtime fans might be hoping for.

Conversely, the Vision is a fascinating construct from the moment he appears on screen, one that seems deserving of even more attention than he ultimately receives, despite being quite pivotal to the goings-on. Whedon clearly has great affection for the character and, aided by the otherworldly mystique provided by Bettany, the Vision carries great promise -- but he arrives with a slightly murky creation story (I didn't entirely get it until a second viewing of the film) and is given what feels like a disproportionate amount of screen time given his potent sense of intrigue. Audiences will likely find the character quite compelling, yet not quite know what they're supposed to make of him when all is said and done.

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Even when a few elements of "Age of Ultron" aren't 100% effective, there are some sublimely successful sequences: on a character level, the early scenes at Avengers Tower with the teammates letting down their hair to enjoy a significant victory works like absolute gangbusters, using the actors' palpably chummy chemistry and our own familiarity with their by-now-well-established personas to terrific effect again; on an action level, the hotly anticipated throwdown between a rampaging Hulk and a Hulkbuster-armored Tony Stark is epic and exhilarating, and made even better when -- as in much of the movie -- the wholesale destruction is underscored with a driving need to protect and save as many civilians as possible -- as in his previous Marvel film, Whedon constantly gives human faces to the vulnerable bystanders the heroes hope to keep from becoming casualties.

And that's in line with the philosophy that's been at the core of the Marvel credo ever since Stan Lee had the big idea to graft real human feelings and foibles onto the stalwart superpowered set all those decades ago: with great power comes great responsibility, a down-to-earth axiom that's defined the exuberantly human heroes of the MCU (even if the original guy who said it on Stan's behalf, Peter Parker, hasn't popped up there -- yet). Of all the things Whedon gets right about Marvel -- and he gets so many things right -- it's the thing he gets right-est. And just as we do with the Avengers themselves, it's the thing that makes it easy to overlook some minor flaws and focus on the bright, positive, powerful things at the core.

The Avengers preparing for battle against a swam of Ultron in Avengers Age of Ultron
Avengers: Age of Ultron
Action
Adventure
Science Fiction
7
10

When Tony Stark and Bruce Banner try to jump-start a dormant peacekeeping program called Ultron, things go horribly wrong and it's up to Earth's mightiest heroes to stop the villainous Ultron from enacting his terrible plan.

Release Date
May 1, 2015
Director
Joss Whedon
Cast
Robert Downey Jr. , Chris Evans , Scarlett Johansson , Mark Ruffalo , Chris Hemsworth , Don Cheadle , Elizabeth Olsen , Paul Bettany
Runtime
2 hours 21 minutes

"Avengers: Age of Ultron" arrives in theaters May 1, 2015.