Three years ago, the Marvel Studios experiment came to a head in Avengers Assemble. Everything they had built and every risk they took along the way led them to an unlikely coming together of larger than life characters who could not be more different to one another.

The Avengers assembled thanks to the deft touch and boundless wit of Joss Whedon, who realised Marvel's dream of seeing Iron Man, Captain America, The Hulk and Thor team up on the big screen. The result was the third highest grossing film of all time.

Marvel had more than monetary success on their hands however, they were also rewarded with an opportunity to continue building a sprawling interconnected series of films based on numerous Marvel properties, and over the past three years they've made three hit sequels and an original - last year's Guardians Of The Galaxy – another unlikely cinematic feat that proved a huge box office success.

Now Whedon returns to assemble his team once more in Avengers: Age Of Ultron, and the results are at the same time familiar, different and as thrilling as ever before.

The pace of the opening act is breathtaking, beyond even the first set-piece and into the set-up of Ultron and the Avengers first attempt to take him down. The first 45 minutes to an hour just about pulls off juggling that speed with a supersized dosage of plot. You don't need to have an understanding the previous films, but a somewhat good memory of the first Avengers is helpful (it is a sequel after all).

Said plot sees Tony Stark (Robert Downey Jr) inventing "a suit of armour" around the world, only to accidentally create Ultron (James Spader), an advanced artificial intelligence with major anger management problems, not to mention daddy issues. Created with world peace in mind, Ultron soon decides the best way for that to happen is the eradication of the human race, which to be fair would put an end to war.

Avengers Age of Ultron
The Avengers assemble once more. Marvel Studios

All the whizz-bang of the first hour makes it essential by act two that the film take a break – and it is here Age Of Ultron first assures us of its top quality. What we see until that point boasts tight direction, memorable set-pieces and cinematography well beyond that of the original film, but what the film needs is a connection to reality, something relatable, and we get it through one simple but beautiful twist.

In terms of character development the film is impressively even-handed. We take a look at Black Widow's (Scarlett Johansson) tragic origins, we get further insight into the troubled mind of Bruce Banner (Mark Ruffalo), Hawkeye (Jeremy Renner) is given depth and the twins - Scarlet Witch (Elizabeth Olsen) and Quicksilver (Aaron Taylor-Johnson) - are given a good backstory on their way to becoming fun additions to the ensemble despite their somewhat iffy accents.

We also see more of Stark's inner-struggle following the events of the first film, and how his character also informs that of Ultron. Only Thor and Captain America don't have much of an arc. For Thor this is a slight oversight, but Cap had his own film in 2014 and will get another next year – so it makes sense. Despite this, nobody ever stands out over anyone else and nobody is left struggling for screen time, every character is given ample opportunity to shine.

Another complaint that could be made is that Ultron should have been given more of a chance to shine than anyone else - he is in the film's title, after all. Spader still makes for a charismatic villain who revels in combating the "android that wants to kill us all" archetype. He isn't a cold, emotion-less robot, he's an impulsive, rage-filled maniac, and all the better for it.

After seven years of the Marvel Cinematic Universe (MCU) it is quite strange how "normal" a film with all these bizarre characters can feel. This is not to say that the film is not exciting or without unexpected twists, but after so many outrageous superhero movies there is a sense that very little will really surprise audiences any more.

Avengers: Age of Ultron
Iron Man dons his Hulkbuster armour to take down The Hulk. Marvel

Which is why the handling of one particular new character was a highlight. Paul Bettany's appearance as The Vision is little more than an extended introduction to the character, but it is an impressive one of importance to the plot, and he gets a fair share of the film's plentiful array of memorable lines and moments. He's also wonderfully weird.

If nothing else, 2012's Avengers Assemble felt special. It was the payoff of an experiment that has since shaped blockbuster Hollywood. Age Of Ultron was never going to recapture the same sense of joy we all felt seeing Hulk fight Thor, Thor fight Iron Man and them all fight together, which makes it feels more like the next chapter in an established and quality series rather than an event we have been building to for years.

That is no criticism. Seeing the Avengers fight alongside each other will never get old, and in Age Of Ultron we see how their now-established relationships are growing and being tested. Whedon's script sells us completely on this unlikely bunch truly being friends and in turn this makes their existence in each other's lives seem more natural than ever.

This may be a somewhat darker film but Whedon's sharp and funny wordplay is still deeply rooted in a script that never forgets the base humanity that brought each of these characters to this stage and which in the new characters gives Marvel the chance to do so again.

Exhilarating and smart from beginning to end, and with the self-awareness that has been a constant in all Marvel's films, Age Of Ultron is a sure sign that Marvel Studios' runaway train has no chance of slowing down any time soon as we hurtle towards the "end-game" of Avengers: Infinity War in 2018.

Film Star Rating Five Stars