After the origin stories, the sequels sliding all over the quality spectrum, one Civil War, a Ragnarok, an Age of Ultron, and a gazillion buckets of popcorn sold the world over, the Marvel Cinematic Universe ascends to a state of supernova in Avengers: Infinity War.

This is the one with every thus-far-established Marvel champion thrown in for the hell of it: not just all the pre-existing Avengers, but some freshly fledged reinforcements, such as Chadwick Boseman’s Black Panther, Benedict Cumberbatch’s Doctor Strange, and Tom Holland’s new Spider-Man. If there were a Marvel superhero called Kitchen Sink, he’d also be in it, and not looking forward to the washing up.

In fact, not every possible character makes an appearance, but on this, as on the fates of the featured many, no more must be said: such is Marvel’s feisty war against spoilers. (Practically mention their breakfast preferences these days and expect online disembowelment.)

For the original triumvirate – Robert Downey Jr’s Iron Man, Chris Hemsworth’s Thor, and Chris Evans’ Captain America – it’s been a decade-long trail to this communal crossroads; for some of the others, barely a year. But the massed collision certainly wants impact: it’s the rangiest, busiest Marvel flick to date and, at 160 fairly breakneck minutes, the longest, too.

Returning to direct are the Russo brothers, responsible for the last two Captain America films, which had a breadth of plot and relative seriousness of ambition not universally shared in the mythos.

The job they and their regular screenwriters have this time is to push those qualities forward while finding space in the stable for everyone else: there’s a lot of self-spoofing and irreverence jostling to get noticed. Jokes, memes and call-backs to other jokes and memes fly around as frenetically as all the whizzy projectiles hurled down from distant planets. Organisationally, the movie has a struggle on its hands not to seem like the contents of a toy chest simply chucked down the stairs, with all the chaos of limbs and accessories that implies.

Chris Pratt as Star-Lord in Avengers: Infinity War

The villain, against whom every one of these galactic guardians is arrayed, is Josh Brolin’s Thanos, and he needs to be a huge, huge deal or the film can’t work: if this lot have handled anything remotely his equal before, there’s hardly the need for such an all-points call-up.

Lo and behold, he has fairly comprehensive plans for pulverising the known universe, using a gauntlet into which six different jewels known as Infinity Stones first need placing, each one distinctly enhancing his power in battle. Close observers of Marvel lore will already know where every one of these coloured rocks is to be tracked down – one’s embedded in the forehead of Vision (Paul Bettany), another around the neck of Doctor Strange, and so on.

Robert Downey Jr., Mark Ruffalo, Benedict Wong, and Benedict Cumberbatch in Avengers: Infinity War

Given the vast scale the Russos are working on, resorting to your typical collect-the-gems plot game seems disappointingly basic, but there’s a thornier problem with Thanos in general: he’s a huge hulk of a being, twice human size, but the effects job on Brolin thwarts his usual authority as an actor.

He can’t scan as a profound adversary, more like some outsize ogre-thug beamed in from World of Warcraft. A subplot involving his adopted daughter Gamora (Zoë Saldana), whom he kidnaps away from her Guardians of the Galaxy cohorts, labours to give him depth, but you feel the effort, and these are the stodgiest scenes.

Thank heavens, then, for his skull-faced wizardy sidekick, one Ebony Maw (Tom Vaughan-Lawlor), who drawls his dialogue with a campy British accent and glides around manipulating rubble with his unnerving fingers. He’s like the shade of Peter Cushing doing a narrating stint on Tales from the Crypt. The movie could do with more of him.

Avengers: Infinity War

The Russos are on much firmer ground pitting their good guys against each other – for comedy or friction – than pushing any of them up against Thanos. Such is the profusion of lately added characters that plenty of them haven’t met yet, and these introductions are reliably good value: the best line in the film, just about, is simply Captain America saying his own name.

Chris Pratt’s alpha status as “Star Lord” Peter Quill takes an amusing hit as soon as Thor, with his vastly more impressive macho credentials, boards his ship: once again Hemsworth is hard to beat in the part for mock-heroic charm with genuine soul nested beneath.

Holland remains a sparky asset, and there’s good stuff with Mark Ruffalo’s Hulk getting attacks of performance anxiety, and Danai Gurira’s proud Wakandan warrior Okoye shooting withering glances at her alleged new allies.

The exorbitant action scenes hit all the necessary crowd-pleasing buttons at regular intervals, but for a movie with infinite potential – Doctor Strange, who gets a good look-in, counts 14 million possible outcomes to the final battle – it’s possible to feel they banked on a rather narrow algorithm.

Death rears its head as something even Avengers might legitimately fear, but it says a lot about this film that one mid-ranking character actually dies twice, and the options for resurrection by the end are almost too multitudinous to get your head around.

One thing’s for sure: it leaves absolutely no doubt that Avengers 4 is going to contain some serious avenging, even if it also hits control-Z on the shock-horror finale that will be the dominant talking point of this one. Solving a problem like Thanos is clearly more than these heroes – or the Russos, quite – have managed in a single try.