Just when it feels like the superhero genre needs a breather, along comes Robert Downey Jr. again as billionaire motor mouth Tony Stark, a.k.a. Iron Man. Like the 2008 original film, “Iron Man 2” flourishes when Downey banters with equally entertaining talents of Gwyneth Paltrow, Samuel L. Jackson and franchise newcomers Don Cheadle and Sam Rockwell.

And yes, kids, there are also a couple of cool action sequences.

Unfortunately, “Iron Man 2” has too much plot and not enough of the fun stuff. The film’s midsection sags with meandering subplots, and the story sometimes feels like a roadmap into another sequel.

The story picks up six months after the events of the first film, when Stark announced to the world that he was the man behind the iron-plated hero. His loyal assistant, Pepper Potts (played with spunk by Paltrow), has been promoted to CEO of Stark Industries, and Stark meddles in his science lab, hoping to find an alternative power source for the mechanism that works as his heart. The current battery is poisoning him, causing weakness, gross black veins and extreme belligerence when mixed with hard alcohol.

The U.S. government also wants Stark to hand over the Iron Man suit, putting Stark’s military best bud, James Rhodes (Cheadle, replacing Terrance Howard from the first film) in an uncomfortable position. Stark has a new assistant (Scarlett Johansson), who may be a spy working for the super-secret government agency S.H.I.E.L.D., led by one-eyed Nick Fury (Jackson, doing his signature brand of Awesome in a couple of scenes).

And don’t forget the bad guys: Rival weapons industrialist and all-around sleazeball Justin Hammer (Rockwell) and Russian roughneck Ivan Vanko (Mickey Rourke), who holds a bitter family grudge against the Stark family. When he’s flipping around some electro-powered whips, he goes by Whiplash.

With so many characters, “Iron Man 2” has a lot of stories to establish. At least you can credit screenwriter Justin Theroux (“Tropic Thunder”) with keeping the long setup snappy. As dispensed from the mouth of Downey, born to play the hard-living, womanizing egomaniac, the dialogue is as fast and fresh as a Tarantino film.

Downey is surrounded by A-list actors, and the film uses them to better establish the flaws and redemptive qualities of Tony Stark. The best scenes involve Paltrow, an actress who can go 10 rounds with Downey’s rapid-fire meandering without breaking a sweat. Pepper serves as Starks’ conscience, constantly challenging his irrational ideas and extravagant selfishness. Without her, Stark would be passed out-drunk whenever the world was in peril.

Returning director Jon Favreau (who also has an amusing supporting role as Stark’s bodyguard) clearly knows how to utilize the talent pool. If only he didn’t feel the need to “top” the first film with an overcomplicated storyline.

While Rockwell is given plenty of screen time to ooze evil, Rourke has little to do with the one-note Whiplash. Johansson tries her best with her unnecessary subplot, and even Cheadle seems underutilized in what turns out to be the film’s most important storyline. There could be an entire movie made out of Cheadle and Downey trading insults, but “Iron Man 2” only provides a few priceless minutes. Comic fans should at least be satisfied with the film’s climax, which sends Cheadle out in full War Machine mode and gives Johansson’s Black Widow an acrobatic fight sequence.

“Iron Man 2” spends a lot of time establishing S.H.I.E.L.D., the agency that will become the focus of the inevitable “Avengers” movie that teams Iron Man with the likes of Captain America and Thor. As fun as that is for comic book fans, it’s hard to expect an audience to get excited for a movie that remains years away from completion. A little bit of foreshadowing works fine, but the rest of the movie should be focused on sustaining and completing its own narrative.

For that, “Iron Man 2” doesn’t quite match the fun of the first film. But it still gives Downey plenty to talk about, and a summer blockbuster so focused on talking instead of explosions shouldn’t be dismissed so easily.

Grade: B