Warning: This review alludes to aspects of the plot.

Tony Stark never said he was deep, nor is he and nor, alas, is the Marvel Cinematic Universe, now at the dawn of its second age. Shane Black was writing Tony Starks, likable smart asses, long before Robert Downey Jr was sober, and he’s lost none of his spark, nor the ability to plot an ebullient actioner but even he, the man who once sold the fuck laden, ultra-violent and misogynist Last Boy Scout screenplay for $2m, can’t get dirty in this studio’s sandbox.

Vast as it now is, you won’t find any grit in there either. Marvel have cornered the market in colourful and empty; the latest Iron-flick is just more product. There’s a lot of fun to be had but these aren’t movies you can return to; there’s little to be discovered on second viewing. Of course it sometimes feels like a second viewing thanks to the importation of scenes from Black’s greatest hit, Lethal Weapon 2 – the assault on the hero’s ocean front property, a showdown at dockside, but that’s cheating: we should want to re-view this one on its own contents.

What does Robert Downey Jr add? If the domestic box office is to be believed, about $130m. Is this Iron Man or any of its predecessors innately more satisfying than any other horse in the Marvel stable? Why is this Avenger so far out in front? Perhaps Stark’s got better tech and more vicarious capital, after all there’s not a teenage boy alive who doesn’t want to play with a weaponised suit and a billionaire’s train set (though the girls get a brief go in this instalment, just to be sure the entire audience is satisfied), but Black’s bit of Marvel mongering is much like all the others when you strip away its star’s easy charm and snappy one liners. It’s breezy, upbeat (despite the terrorism) and wholly inconsequential.

This third Iron Man is a better film than part two, assuming you can look at Jon Favreau’s series in isolation; it’s less cluttered, more intimate; but any hope that this post-Avengers cycle would cut deeper than the first is a pipe dream. Marvel’s employed a core vote strategy with this movie: it’s about keeping the audience they have rather than building on the one they’ve got.

That deflating fact notwithstanding, Black can claim, with some justification, that he’s made a more character focused, more low-key addition to the Marvel storyline than The Avengers. It’s not quite deep enough to be an introspective hangover but the assured scribe has peppered his story with nice touches. The film gives the usually self-assured hero something of an existential crisis, for a time he’s partnered with that Hollywood rarity, a likable and quick-witted child (no sentiment, some irony), and there’s an original spin on that reliable comic book staple – the hero and villain as two sides of the same coin. Both Stark and Guy Pearce’s Aldrich Killian act as remote puppeteers in Black’s story – a conceit that allows for more than a few satisfying rug pulls. In other words, even at this late stage of the game, the one time golden boy of Hollywood action cinema can find ways of keeping this series fresh and surprising, without spooking the horses.

Iron Man 3 is a bit of a frolic, then; great while it lasts and forgettable thereafter. We’d kill for the full Shane Black experience: the winning trio of violence, language and nudity, but this entry-level version for kids with colourful lunchboxes will do in the meantime. Those with an interest in Hollywood’s outreach activities toward China and its ever growing army of multiplex zombies, will note they’ve sunk some Yuan into this piece of Americana and have been duly rewarded with an orientally-affected villain. If you’re lucky enough to live under Communist rule you can even see some additional scenes featuring Wang Xueqi and Fan Bingbing. Still, British fans can’t complain: both the humble London suburb of Croydon and TV series Downtown Abbey get namechecked. This is a truly international blockbuster…provided you live in a key market that is.