Since its announcement in May 2012, speculation as to whether writer-director Joss Whedon could do it all again and create a blockbuster sequel to 2012’s The Avengers was rife, along with questions about which Marvel characters would be next to make the leap from page to screen. Avengers: Age of Ultron sees the return of Iron Man (Robert Downey Jr), Thor (Chris Hemsworth), Captain America (Chris Evans), Black Widow (Scarlett Johansson), The Hulk (Mark Ruffalo) and Hawkeye (Jeremy Renner), as well as introducing some new heroes to the fight to save the world. But has it been worth the wait?

In the fictional Eastern European city of Sokovia, the Avengers team are working hard to break into Hydra and retrieve Loki’s sceptre with their usual gusto. They had it in the The Avengers, but since then, there has also been Iron Man 3, Thor: The Dark World, Captain America: The Winter Soldier, Guardians of the Galaxy, Agents of S.H.I.E.L.D. and Agent Carter, so presumably someone just misplaced it. With agents of both S.H.I.E.LD. and Hydra switching sides quicker than you can blink, it would have been easily done.

Last shown in confinement being watched over by Baron Strucker (Thomas Kretschmann) during the mid-credits scene in Captain America: The Winter Soldier, it now turns out that twins Pietro and Wanda Maximoff (Aaron Taylor-Johnson and Elizabeth Olsen) volunteered to be experimented upon by Hydra. Genetically enhanced to become Quicksilver and Scarlet Witch respectively, they seek vengeance on Tony Stark for the death of their family and obliteration of their village by bombs bearing his company name – Stark Industries. Understandably – I think I’d be a bit angry too.

But Age of Ultron is not all action. Similar to the end-credits “shawarma” scene in The Avengers, there are some genuinely heart-warming moments where the Avengers and company just kick back and relax. One such scene happens after a house party at Stark’s to celebrate finally getting hold of Loki’s sceptre, and sees them all come together to play that famous drinking game, “Who Can Lift Mjolnir?” With no winners (or at least none that Thor’s ready to admit), the after-party continues.

It’s in this jovial scene that the movie’s villain Ultron (James Spader) announces his sinister presence, dragging in the first of his many metallic bodies. With leaky parts and a consciousness stolen from J.A.R.V.I.S., Ultron replays Stark and Banner’s conversation of an artificially intelligent peace-keeping project to the group before attacking them with controlled Iron Legion robots. Disappearing through the internet, Ultron’s eerie sing-song voice of “I have no strings to hold me down, there are no strings on me” echoes as he enacts his version of a peace-keeping plan: saving humanity from itself by completely destroying it. Great plan, Ultron. Repeatedly bounding over the line between evil madman and pantomime villain (well, he is part-Tony Stark’s personality) throughout the film, Spader’s performance as Ultron is absolute perfection.

The slow trickle of names revealed to be attached to this film have continued flowing right up until its final release. How they found room to add more names to the already ensemble-heavy movie poster without breaking the rules of Marketing 101, perhaps we’ll never know. Rumours ran amok about characters reprising their roles from previous Marvel films, and about brand new characters yet to be seen. While James Rhodes (Don Cheadle), Erik Selvig (Stellan Skarsgard) and Sam Wilson (Anthony Mackie) all have short-but-sweet cameos, Heimdall (Idris Elba) and Peggy Carter (Hayley Atwell) only appear in trippy, Scarlet Witch-induced dreams.

Paul Bettany, who in previous films has only been present as the disembodied voice of J.A.R.V.I.S., now finally gains a  physical form as Vision. Vision’s appearance has up till now been kept a closely guarded secret, with the character represented by a strategic, shadowy blur on the movie’s official poster. It turns out that, like with all mystical objects, it wasn’t actually Loki’s sceptre that held power – it was the Infinity Gem within it. Remember the Infinity Gem from Guardians of the Galaxy? Well, it’s pretty important here, since this one gets lodged in Vision’s forehead. Created as the final vessel for Ultron to occupy and stolen from Ultron by the Avengers, Vision endures a perilous game of pass-the-parcel before being finally activated by Thor’s hammer. With Vision brought in for the final act, adding to the weight of so many characters already, it does feel as though that they need not have bothered with all the secrecy. As a confusing mix of J.A.R.V.I.S., Ultron and something not quite either, Vision is yet another omnipotent, benevolent character with a cape. Where will he turn up next? Maybe he’ll come back for another film, but it doesn’t feel like a pressing question.

Hinted at in the trailer, the romantic sub-plot between Natasha Romanoff and Bruce Banner is unfortunately an underdeveloped weak link in Age of Ultron. Romanoff is first introduced to Banner when she is sent to recruit him in The Avengers for the Avengers Initiative. Once onboard S.H.I.E.L.D.’s helicarrier, it’s not long before Banner transforms into The Hulk and TRIES TO ATTACK Romanoff. And that’s just two of the very few interactions seen between them. There was previously so much geared towards implying that Romanoff had more-than-friends feelings for Hawkeye, that establishing Banner as a love interest for Romanoff to get doe-eyed over felt forced and out of nowhere. It’s also a little frustrating that Whedon, renowned for his “strong female characters”, has played this with such awkward footing: within an almost all-male team, Black Widow has proved herself a rich and resilient character, with no need of being neatly paired off with a fellow Avenger.

Speaking of surprise love, Hawkeye now has a wife and children! A little farmhouse with lush acres of surrounding fields is where this bow-and-arrow-wielding Avenger calls home, with wife Laura (Linda Cardellini) and his two-soon-to-be-three kids. Giving more screen-time to Jeremy Renner pays off in magnitudes. Not all of the Avengers are gods or genetically altered, some of them are very human with the exceedingly human ability to die. In the scene with his wife, we get to see what true cost there is for all of the Avengers in continually fighting to save Earth. This exchange gives meaningful weight to both Hawkeye’s pep-talk with Scarlet Witch during the final battle and the direction of the franchise to come.

A deliberate mid-sentence scene cut amusingly signs off Joss Whedon’s fantastic contribution to the Marvel Cinematic Universe. Weaving together the already epic plots of comic-book characters into two unlikely stories and carefully nudging the direction of their spin-off films and TV shows, Whedon has been shaping the world like a real-life Nick Fury and has made cinematic history.

At just under two-and-a-half hours long, Age of Ultron is another Marvel bum-number but the action is so cautiously paced that you’d never know. If you do get the chance to see this film in IMAX 3D as I did, do it: every shot is spectacular.

Avengers: Age of Ultron is out in UK cinemas on April 23.