Warning this review contains spoilers

Everyone must be aware by now that there is a group of fictional superheroes known as the Avengers knocking about. There must be amoebas on Titan who know that Robert Downey Jr is charismatic as Iron Man and that Chris Evans is strangely likeable playing Captain America. The Avengers have become a part of our cinematic landscape, along with being quietly disappointed about the number of sequels/adaptations and the lack of original films.

Now the Avengers we know (Iron Man, Thor, Captain America, Black Widow, etc.) and a few new ones (Quick Silver, Scarlet Witch, The Vision) are back and have teamed up to fight a new big bad in the form of Ultron, a psychopathic machine intelligence that is intent on destroying humanity.

Avengers: The Age of Ultron is an action movie at its heart, and it certainly does not lack for gripping action scenes. There are at least five spectacular fight sequences scattered throughout the film, each one more impressive and dazzling than the last. Avengers: The Age of Ultron is a movie that makes full use of the cinematic toolbox to create a treat for the eyes.

My personal favourite action sequence is fight mid-way through the film between the Hulk, ably played by Mark Ruffalo, and Downey Jr's Iron Man in a new extra large suit of armour. Superhero crossover movies are at their most fun when the heroes fight each other, as it settles the questions teenage geeks spending hours pondering: who would win in a fight between X and Y. This kind of drama is not the basis for Shakespearian intrigue, but it does make for spectacular viewing.

As a science fiction film, it has to be said that this is a little light on the science. It is still not clear if Thor is an actual magical god-being or an alien, and characters like The Vision are more fantasy than science fiction. However, James Spader’s Ultron is a brilliant villain, an out of control AI without a care for human suffering, intent of improving the world by destroying it. This is not original writing – the basic plot is little different from Terminator or The Matrix – but I have a weakness for AI-run-amuck films and Avengers certainly delivers this. Spader excellently camps it up as the evil Ultron and clearly loves every minute of being the villain.

A film that has the combined cast of four other films is understandably overflowing with characters, and writer/director Joss Whedon ensures that they all get their moments and all get a character arc. The best of these is Quick Silver’s and Scarlet Witch's redemption arc as they both begin the movie in the service of Ultron and then go over to the Avengers when they see how evil he is. This is nimbly handled and had some great acting from Elizabeth Olsen and Aaron Taylor-Johnson in their respective roles.

Every character’s role is weaved into the plot of the film, but I was left feeling that some were not necessary. The cast is perhaps too large and the pace would have suffered under a less capable director. Hawkeye, The Vision and Black Widow could have been jettisoned and the film would have been improved, although the removal of the latter would mean that there was only one woman with a substantial role in the film.

Cutting the number of characters would have left more time to develop the ones that remained. The arcs of characters such as Thor and Captain America are rushed, and at times barely coherent. In an ensemble superhero film, less is certainly more.

This lies at the heart of what most disappointed me about Avengers: The Age of Ultron. I was left feeling that Whedon was more committed to bringing in as much of the wider Avengers franchise as possible than to making a good film. Whedon has worked with ensemble casts before and handled their arcs and characterisation much better. For example, Serenity also has an established ensemble cast, however in that film each is given several moment to shine, where as in Avengers: The Age of Ultron characters such as War Machine and the Falcon are hardly in the film, which makes me wonder why include them at all other than to give the audience a knowing nod to the other films in the Avengers franchise.

Audience love knowing nods: it makes them feel clever and part of a club, and everyone loves that, but knowing nods do not make a good film. Developed characters and interesting scenes make a good film, but clearly this was not the priority when making the Avengers: The Age of Ultron, or there would be less cameo appearances and more time spent on developing the core characters. For example, an extended segment exploring Hawkeye's domestic situation was dull and pointless, but apparently necessary. Cutting Hawkeye would have allowed more time to develop more interesting characters, such as Thor and Captain America.

Whedon does make all of this work and also brings his trademark humour to the film, which makes it hugely enjoyable to watch. Avengers: The Age of Ultron takes itself a lot less seriously than Batman and is all the better for it. Witty lines pointing out the absurdity of the whole film make it more believable than trying to earnestly sell the conflict between a man in a clown suit and a man dressed as a bat as a deep meditation on the human condition.

However I do feel that Avengers: The Age of Ultron takes itself too seriously and tries to make all the characters relatable, which is not necessary. The audience’s lives are nothing like those of Tony Stark or Steve Roger, so why do we have to relate to them via their personal lives? Avengers: The Age of Ultron is an action movie and great action movies of the past, such as Alien or Predator, were lighter on character development and better on motivation - basic survival - and they are stronger movies for it.

Despite these weaknesses, Avengers: The Age of Ultron is a brilliant rollercoaster of a film. It is funny, has good actors, great writing and amazing visuals, it will certainly be the best superhero film of the year – and maybe the best sci-fi/action movie of the year if Star Wars 7 is more Phantom Menace than New Hope. I would highly recommend that any fan of superhero, sci-fi or action movies head down to their local multiplex and see Avengers: The Age of Ultron.