The law of diminishing returns has long been an affliction of the modern movie franchise, wherein bigger is believed to be better and the script often resembles a paint-by-numbers exercise in calculated cynicism.

The rust appeared to have set in for Ol’ Shellhead with the turgid Iron Man 2, a vacant mess as bloated as its director John Favreau that undid all of the good work of the entertaining first instalment.

However, the mojo is back thanks to another bold decision by the powers that be at Marvel (following the call to appoint Kenneth Branagh to direct Thor) to take a punt on meta-man Shane Black to co-write and helm the studio’s first salvo since Joss Whedon’s Avengers Assemble struck box office platinum.

Anyone familiar with Black’s only previous stint in the director’s chair, 2005’s Kiss Kiss Bang Bang will know getting him on board for Iron Man 3 makes total sense. For one thing, Kiss Kiss Bang Bang starred Robert Downey Jr (in something of a career comeback performance), whose rapid-fire delivery fitted Black’s snappy, wise-cracking dialogue to perfection.

It therefore shouldn’t come as a major surprise to learn that Black has a blast with Tony Stark (Downey Jr), the ingenious, fast-talking billionaire egotist and self-appointed superhero who must go back-to-basics and overcome his post-Avengers Assembled panic attacks when his cosy world is turned upside down at the hands of the Mandarin (Ben Kingsley), a megalomaniacal terrorist seemingly hell-bent on bringing America to its knees.

Although there are obligatory boxes that need ticking when dealing with a franchise picture, there are more than enough Blackisms peppered throughout the film’s 130-minute running time. While Whedon got away with one truly inspired moment in Avengers Assembled when a crew member on S.H.I.E.L.D’s flying aircraft carrier is caught playing classic video game Galaga, Iron Man 3 is all Black.

He has a field day pulling the rug from under the viewer by undermining familiar screenwriting tropes, such as in the amusing relationship between Stark and troubled kid Harley (Ty Simpkins), who helps him get to the bottom of the Mandarin’s dastardly plan. Black knows we’re expecting a father/son bond to form, but buries the notion in a blizzard of cute one-liners.

Likewise, he saves some of the best lines for the smart-suited henchmen, who in any other blockbuster outside of an Austin Powers flick would be nothing more than target practice for our hero.

To Black’s credit, he and co-screenwriter Drew Pearce keep Tony out of the heavy metal suit for long periods (even during the inevitable robots-hitting-each-other final reel), no doubt understanding the franchise’s greatest strength isn’t the wham-bam special effects (although there’s still plenty of them), but rather Downey Jr’s scenery-chewing performance.

That being said, Downey Jr’s turn is so big many of the supporting cast barely have a chance to make an impact, especially Gwyneth Paltrow as Tony’s soul mate Pepper Potts, who looks confused or shocked most of the time, and Rebecca Hall as Stark’s former conquest Dr Maya Hansen, who has so little to do it’s almost tragic.

Don Cheadle gets a lot more to do this time around as Rhodes, whose Iron Man suit has been sprayed red, white and blue and renamed Iron Patriot (as opposed to its previous moniker, the more honest War Machine) and who gets to enjoy some Lethal Weapon-style buddy action with Tony, which is only appropriate bearing in mind Black wrote that 80s blockbuster.

The only one who truly stands out alongside Downey Jr, however, is Kingsley, who steals every scene he’s in as the mysterious Mandarin. It’s a superb, multi-layered performance that’s as out-there as it is memorable.

One of the problems with creating a post-Avengers universe containing a big green guy and a hammer-wielding god is that they’re notable by their absence in Marvel’s stand-alone movies. The film tries to get around this big, gaping logic hole when Stark explains: “This isn’t superhero business. It’s American business.” But if that’s the case, then where’s Captain America?

As with Kiss Kiss Bang Bang and Black’s numerous other scripts (in particular The Last Boy Scout), Iron Man 3 gets a little too-cute for its own good, to the extent whereby some scenes get so caught up in the next one-liner the narrative grinds to a halt.

That being said, the direction Black and Pearce take the main character is a real winner. This Tony Stark must swallow his pride, understand the consequences of his actions and rely on the skills that created Iron Man in the first place if he is going to prevail.

Whether this is Downey Jr’s final solo stint as Ol’ Shellhead remains to be seen; either way Black has forged a Marvel-ous summer blockbuster that’s as cool, collected and cocksure as its hero.