Iron Man 2 (Paramount Pictures and Marvel Entertainment), opens with a nice little allegory about its own sequel anxiety. At the Stark Expo, a World's Fair-like celebration at a corporate park in Queens, the weapons-mogul-turned-superhero Tony Stark (Robert Downey Jr.) makes a spectacular airborne entrance in his titanium suit, alighting on an arena stage before thousands of cheering fans. But once he lands and sheds the suit, Tony doesn't know quite what to do. Now that his secret identity has been revealed and world peace achieved, he's reduced to strutting in the spotlight, singing his own praises with mock humility. The first installment of Iron Man traced the billionaire playboy's transition from alienated bon vivant to anti-weapons activist. Now that the Pax Ironmaniana is upon us (as Tony boasts to a Senate subcommittee, "I have successfully privatized world peace"), the hero, and the franchise, are dependent on outside conflict to justify their enormously expensive existence.

That conflict comes along in the form of Anton Vanko (Mickey Rourke), a Russian physicist and ex-con who—for reasons that Samuel L. Jackson will pop up late in the movie to explicate—is Tony's sworn nemesis. While the world's rogue nations incompetently attempt to copy Stark's impregnable suit, Vanko manages to devise a working model, funded by sleazy defense contractor Justin Hammer (the insufficiently famous Sam Rockwell, having the time of his life).

Rourke, as an actor, is the anti-Robert Downey. Where Downey flirts and courts, making the viewer feel as though we're riding shotgun in his sports car en route to the best party ever, Rourke always seems to be receding, withdrawing to a place where something's happening that's too deep and dangerous for the viewer to understand fully. He's a mesmerizing actor to watch, and the difference in style between the two could have made for a fascinating clash. But the actors only get two scenes together, and during the second one, they're almost entirely encased in metal suits and masks. It's beyond absurd that the makers of superhero movies haven't grasped this yet: When an actor's body and face aren't visible beneath a costume, it could be anyone under there. Casting the likes of Downey and Rourke and then imprisoning them in jointed refrigerators is resource-squandering of the highest order.

Jon Favreau, who directed both Iron Man movies (and who plays Tony's driver and sidekick, Happy Hogan) barely conceals his impatience with the action sequences. There are three big ones in this movie, one per act, and the moment each one begins, the film's energy plummets. (The climactic scene in particular, a long battle involving an army of unmanned drones, feels as low-stakes as a video game.) Don Cheadle takes over Terrence Howard's thankless role as "Rhodey" Rhodes, Tony's straight-and-narrow buddy in the military who pitches in for the final robot showdown. Poor Cheadle looks even more uncomfortable in a shiny metal super-suit than he did in that cowboy getup in Boogie Nights.

Everything worth watching in Iron Man 2 happens when the characters doff the armor and hang out in their civvies. Though the dialogue (by the actor-turned-screenwriter Justin Theroux) is never as screwball-worthy as that of the first Iron Man, there's some snappy interplay between Tony and his second-in-command, Pepper Potts (Gwyneth Paltrow), especially after the luscious Natalie Rushman (Scarlett Johansson) is hired as an executive assistant. Action-wise, Paltrow isn't given a lot to do beyond dithering prettily and awaiting rescue, but ScarJo gets the opportunity to demolish a few villains in her Black Widow catsuit. Rockwell has a hilarious scene in which he lovingly demonstrates the uses of a suitcase full of James Bond-esque superweapons. And a mid-movie interlude explores Tony's descent into drunken self-pity in scenes that can't help but recall Downey's own years as a privileged Hollywood wastrel.

The Iron Man franchise should trust Downey more, trust that we want to hang out with Tony Stark as he putters in his absurdly high-tech workshop or nurses a hangover in a giant plaster donut. The first movie got its reputation as the thinking man's blockbuster for a reason: It relied on Downey's winning, mercurial presence for its firepower. Succumbing to the temptation (or the industry pressure) to ramp up the clanky special effects for the second outing, Iron Man 2 throws away its most irreplaceable special effect.

Slate V: The Critics on Iron Man 2, Babies, and Casino Jack

Like  Slate on Facebook. Follow us  on Twitter.