With 2008's "Iron Man" a solid if uneven addition to Marvel's cinematic superhero legacy, there was the natural belief that a sequel could finally move past the setup phase and delve deeper into the characters and story while rustling up grander action set-pieces. That is how it often works with comic book-inspired movie franchises—at least when dealing with an immediate follow-up to the original—and, with most of the same actors and crew back, there was no reason to expect otherwise. Oh, how wrong one can be. Clearly a victim of being rushed into production before the material was up to snuff, "Iron Man 2" is so overbloated with creaky exposition, ineffectual cast additions and turgid subplots that returning director Jon Favreau (2005's "Zathura") and screenwriter Justin Theroux (2008's "Tropic Thunder") barely have time to realize they're first and foremost supposed to be making a summer action picture. When scenes of this sort finally arrive—and be warned that they are few and far between—they come off as deflating afterthoughts. In one fell swoop, Favreau has driven this once-promising series straight into the ground.

At predecessor's end, Tony Stark (Robert Downey Jr.)—playboy, engineer, and head of weapons manufacturer Stark Industries—announced to the press that he was, indeed, Iron Man. Six months later, Tony is a superstar with the common people, successfully having brought about world peace for the time being. Less of a fan is Senator Stern (Garry Shandling), who fears other countries are creating similar body weapons and wants him to hand over his suit. Tony has a lot on his plate as it is, not the least of his worries being a worsening heart condition that will kill him if he does not invent a new healing element in time. Promoting assistant/love interest Pepper Potts (Gwyneth Paltrow) to CEO of the company and hiring the slinky but tough Natalie Rushman (Scarlett Johansson) as his new gal Friday, Tony begins to wallow in self pity until some bad guys come knocking. Ivan Vanko (Mickey Rourke) wants vengeance, determined to make Tony pay for his father's decision forty years earlier to cut his Soviet physicist dad out of the then-upstart company, while Justin Hammer (Sam Rockwell), owner of a rival, not-as-successful weapons manufacturer, wants to destroy Stark Industries. If that weren't enough, S.H.I.E.L.D. director Nick Fury (Samuel L. Jackson) comes knocking, out to eventually gather up the superheroes of the globe for an epic team known as the Avengers.

A perfectly respectable film could be made from that aforementioned synopsis, but "Iron Man 2" goes down the wrong path at nearly every step. The light, charming interplay between Tony and Pepper is now fraught with tension and arguments, and Pepper has been turned for no apparent reason into a high-strung, shrieking harpy. The villains are as dull as dishwater, with Ivan (also known as Whiplash when he's swinging his electrical switches around) spending the bulk of his time muttering Russian, tinkering around at his workbench, and talking to his pet parakeet. Justin Hammer, meanwhile, is little more than a preppy, wimpy rich kid who gets other people to fight his battles for him. Other new characters, like Tony's assistant Natalie Rushman—really an undercover agent for the S.H.I.E.L.D. organization—vie for screentime while remaining two-dimensional and enigmatic.

There is exactly one action sequence that garners any thrills and fireworks at all—the first confrontation between Tony and Ivan set at the Monaco Grand Prix—and it is out of the way by the 40-minute mark. Why does Tony decide to impromptu race in the competition at all? That's just one of the many nonsensical contrivances the script cooks up. From there, it's all downhill, with way, way too much time spent on Tony becoming a jackass as he alienates those closest to him and boozes it up while waiting for his ticker to give out. There is a particularly moronic scene where Tony and best friend Lt. Col. James "Rhodey" Rhodes (Don Cheadle), both suited up in metal, fight each other and entirely destroy Tony's seaside Malibu mansion to the score of Queen's "Another One Bites the Dust." Who thought this egregious, completely over-the-top development was a good one? Furthermore, why reveal Natalie to be a leather-costumed butt-kicker and then give her all of one peripheral sequence to show off what she's working with? After this, it should be noted, she disappears without another mention and proves pointless to the narrative. The climactic battle, where all of the spare pawns kinda-sorta come together, is anticlimactic in the extreme and has no emotional impact.

Robert Downey Jr. (2009's "Sherlock Holmes") returns to the role of Tony Stark/Iron Man and again brings to the forefront a personality that is pompous with a conscience. The actor's problem isn't his performance; it's just that he doesn't have as many interesting things to say and do this time around. Gwyneth Paltrow (2006's "Running with Scissors") is a little too abrasive as Pepper Potts, harder and less likable than her former self. Don Cheadle (2008's "Traitor"), taking over the part of Jim Rhodes from Terrence Howard, is miscast, losing all of the subtle homosexual subtext in his bland translation of the character. Scarlett Johansson (2008's "The Spirit") is underused to the point of criminality as Natalie Rushman/Black Widow. Sam Rockwell (2009's "Moon") is stuck essaying the boring character of Justin Hammer; he has to be one of the meekest villains in recent memory and has none of the fun of his similar, far superior role in 2000's "Charlie's Angels." Finally, Mickey Rourke (2008's "The Wrestler") looks like he'd rather be anywhere else; his Ivan/Whiplash is played like a caricature rather than a genuine threat, the actor hiding his lack of comfort behind tattoos, an accent, and an aviary sidekick.

When "Iron Man 2" wobbles to its conclusion and peters out with the appearance of the end credits, it's difficult to believe what a trifling waste the past two hours have been. Gone is the effortless mixture of breezy, energetic humor and high-octane action, replaced by dialogue that's not as quick-witted, action that's not as exciting, and a tone that's reserved bordering on mirthless. Additionally, the story is stuffed to the gills, the focus is all over the place, and the general mood of the production is one that curiously feels like it's happening out of obligation rather than inspiration. "What would you do if you knew you were about to celebrate your last birthday?" a ruminative Tony asks Natalie in the film's best moment. "I'd do whatever I want to do with whoever I want to do it with," she replies, her words just about the only wise thing in a distaff movie that's otherwise anything but. After the well-crafted form of the original, "Iron Man 2" plays like a feeble joke that nobody's in on.