Funny, twisty and thrilling, this is shellhead’s most entertaining solo flight to date. It’s also an impressive pace-setter for this summer’s barrage of big movies.

So Phase Two is underway – and in style. After Joss Whedon’s benchmark-setting Avengers ensembler, there was always a danger that the next Marvel stand-alone might feel an anti-climax. So perhaps it’s just as well that Tony Stark (Robert Downey Jr.), just as he was with 2008’s Iron Man, is the one called upon to kick-start this new cycle. The self-described “genius, billionaire, playboy, philanthropist” has always been the Marvel Cinematic Universe’s life and soul (and mouth); but put him in the hands of incoming director/co-writer Shane Black, and he propels this fourth IM outing like a nuke-fuelled rocket.

Based, partly, on the Warren Ellis-penned six-issue ‘Extremis’ arc (2005-06), this opens with a flashback to Switzerland, hours before Y2K arrives. Partying like it’s, well, 1999, Stark is ignoring Guy Pearce’s goofy-looking geneticist Aldrich Killian and flirting with his partner Maya Hansen (Rebecca Hall). Big mistake, as our hero will later discover. Fast-forward to present-day and he’s a changed man. He has his plush ocean-view mansion. He’s going steady with the delectable Pepper Potts (Gwyneth Paltrow). He’s even got a freshly-designed suit that clamps itself, piece by piece, onto his body.

Yet all is not well. Prone to panic attacks in the wake of his close encounter at the end of The Avengers, Stark is also going through a rocky patch with Pepper (which even the 15-foot stuffed bunny he buys her – it is Christmas after all – can’t fix). Worse still, Killian is back on the scene – now the slick, suited tycoon behind A.I.M. (Advanced Idea Mechanics), the brain trust that’s conceived Extremis, a sophisticated method of DNA reprogramming that can repair and regenerate limbs.

One of the early benefactors of Killian’s tech is Eric Savin (James Badge Dale, excellent), a Terminator-like force-of-nature soon responsible for seeing Stark’s faithful chauffeur Happy Hogan (Jon Favreau) hospitalised. It’s part of a US-targeting terror campaign, behind which lurks the shadowy figure of The Mandarin (Ben Kingsley), a hooded fiend with a Bin Laden beard. Eventually, Stark, goaded by reporters, bullishly declares “good-old fashioned revenge”, even offering up his Malibu home address. Second big mistake.

Cue the film’s outstanding set-piece: a helicopter attack on Chez Stark that’s as big and loud as anything in the series to date. Wildly upping the scale on his 2005 directing debut Kiss Kiss Bang Bang, Black proves a sure hand when it comes to delivering comes to delivering juggernaut action (shades of his 1996 writing gig The Long Kiss Goodnight).

But it’s really Black’s scripting nous that makes Iron Man 3 soar – not least in the way the former Lethal Weapon scribe channels the buddy formula he practically invented into Stark’s ongoing relationship with Col. James Rhodes (Don Cheadle). With Black reigniting the spark he cultivated with Downey Jr on Kiss Kiss, the result is snappy, not snarky. Gone for the most part are the self-satisfied barbs that made Iron Man 2 a lead weight. Unshackled, even stripped of his suit for much of the film.

Downey is on fine form here – never more so than in his relationship with Tennessee kid named Harley (Ty Simpkins), who becomes Stark's unlikely ally at a particular crisis point. Forget any sentimental mentoring here. When Harley tells Stark that his father walked out on him six years ago, he tells him to stop being “a pussy”. Harsh – but it gets a laugh.

Meanwhile, thanks no doubt to Black’s British-born co-writer Drew Pearce, there’s even a neat line in Anglo-appreciation – gags about Downton Abbey and Croydon (“wherever that is”, notes Pearce). The British cast members are also a welcome addition; Hall elevates Maya beyond the sexy lab-assistant clone while Kingsley’s ultra-menacing turn as The Mandarin is nothing short of sensational. The master, as one of his security guards notes, is indeed on the move.

So what’s not to like? Well, the 3D post-conversion adds absolutely nothing, apart from some irritating plastic glasses to your face and a layer of murk that renders set-pieces occasionally hard to follow. Coming in at just over two hours, it suffers a few saggy sequences (Rhodes’ detour to Afghanistan, for example) that weigh down the film’s convoluted middle act. Meanwhile, efforts to explore Stark’s troubled psyche don’t go especially far, or yield any great emotional punch.

But Black’s blockbuster satisfies thanks in no small part to a rug-pulling narrative that’ll floor you at least once. Pearce makes up for his virtually non-role in Prometheus, while an ab-flaunting Paltrow finally gets in the action (and is good value for it). Complex and deep it’s not; but as a two-hour adrenaline shot, Iron Man 3 delivers.