The Avengers is the pinnacle of Marvel’s cinematic master plan – an unprecedented team-up of comic book characters that has been painstakingly constructed over five feature films, making this one of the biggest blockbuster events of recent years. In preparation for this long-anticipated occurrence, Marvel have been ambitiously churning out an entire family of interconnected feature films and shorts, beginning with 2008’s hugely entertaining Iron Man and continuing in more erratic fashion with The Incredible Hulk, Iron Man 2, Thor and Captain America: The First Avenger. On paper this cinematic team-up shouldn’t work, with so many characters vying for screen time and an infamously controlling studio overseeing production. But director Joss Whedon has pulled off an *ahem* marvelous feat in balancing this superhero circus, delivering an immensely satisfying film which will charm fanboys and casual viewers alike, not to mention ensure massive box office success for Marvel and their new parent company Disney.

For such a great film, The Avengers gets off to an awkward start. Opening in a secret S.H.I.E.L.D. research facility, physicist Eric Selvig (Stellan Skarsgård, reprising his Thor role) is conducting experiments on the Tesseract, an energy source of unknown potential contained in an opaque cube which was previously used by the villainous Red Skull during the WWII events of Captain America. These experiments open a portal through space, from which exiled Norse god Loki (Tom Hiddleston) steps through, taking down S.H.I.E.L.D’s finest – Director Nick Fury (Samuel L. Jackson), marksman Clint Barton/Hawkeye (Jeremy Renner), and Agent Maria Hill (Cobie Smulders) – with relative ease and escaping with the Tesseract. While it’s a perfectly acceptable place to start, the execution is off; compared to the rest of the film, the opening sequence is humourless, constrained and uninvolving.

However things quickly pickup once Loki is out in the world and S.H.I.E.L.D. are forced to implement “the Avengers Initiative”. Sexy super-spy Natasha Romanoff/Black Widow (Scarlett Johansson) is called in to track down brilliant scientist Bruce Banner (Mark Ruffalo), who is living off the radar to avoid triggering his destructive transformation into the Hulk. Super-soldier Steve Rogers/Captain America (Chris Evans), still struggling to adjust to the 21st century, is the easiest to convince thanks to his old-fashioned sense of patriotism, while billionaire inventor Tony Stark/Iron Man (Robert Downey, Jr.) is loath to take time off from his shiny new self-sustaining Stark Tower and girlfriend Pepper Potts (Gwyneth Paltrow). Once the gravity of the emergency sinks in, they all join Fury’s shadowy peacekeeping agency on one of the coolest modes of transport seen on-screen in a long while – a giant and stunningly rendered helicarrier which can become invisible, and on which a majority of the film is set. Asgardian deity Thor (Chris Hemsworth) soon joins them, keen to bring his brother back home to face justice. Of course, the team fail to gel initially, as Stark and Roger’s opposing ideals and personalities cause friction, while Thor’s arrogant arrival triggers a brawl between all three. Banner’s uneasy presence does nothing to calm tensions on the ship, and Whedon’s obvious skill for family dynamics is showcased wonderfully in these frequently hilarious and engaging exchanges. Once the stakes are raised high enough, the Avengers are forced to put aside their differences and band together to save the planet from the megalomaniacal Loki and the mysterious Chitauri army he plans to unleash on an unsuspecting population.

One particular strength of each Marvel release so far has been the casting. Downey, Jr. carried Iron Man with effortless charm, and as expected he gets the best lines here, dispensing sarcastic insults (on Thor and Loki’s bickering: “Shakespeare in the Park”) and fun pop-culture references throughout (on Loki’s outfit: “Reindeer Games“). Jackson finally feels engaged and fuelled with a sense of purpose for the first time in a Marvel film, Clark Gregg’s Agent Phil Coulson is given more than usual to do, and Johansson is almost revelatory this time around when compared to her dead weight appearance in Iron Man 2. The biggest and best surprise of this film is Ruffalo, who takes over the role previously played by Eric Bana and Edward Norton, infusing Banner with an intense and deceptive quietness, and effectively playing the Hulk through performance capture for the first time (voiced by Lou Ferrigno). With the Hulk’s disappointing track record, he could have been written off as the weak link here, but to Whedon’s credit he has deftly turned a problem into one of the film’s great strengths. Unfortunately, the usually great Renner is given little to do, which is problematic since his Hawkeye needs some fleshing out as he only had the briefest of (reshot) cameos in Thor. Smulders’ S.H.I.E.L.D. operative is also given too little development, and she is oddly humourless for a comedienne.

Marvel has had an interesting and diverse approach to choosing directors so far, but none have yet to completely imprint their own unique stamp on a picture, often seeming more like freelancers serving Marvel’s vision. Which makes Whedon – an inexperienced director but revered writer/showrunner known primarily for his cult TV creations Buffy, Angel, Dollhouse and the sorely missed Firefly - seem a potentially risky choice and yet also the ideal one. Whedon is first and foremost a writer (Speed, The Cabin in the Woods), and here he masterfully reworks Zak Penn’s (X2, The Incredible Hulk) script into a compelling, relentless narrative, injecting his trademark wit along the way and imbuing each character with depth, an arc, and moments to shine. He obviously has a passion for, and experience in, Marvel’s comic universe – his great 2004 series Astonishing X-Men reinvigorated the X-Men – and it clearly shows here, as this is perhaps the first superhero film that feels like it was lifted right from the pages of a comic. Taking influence equally from Stan Lee and Jack Kirby’s 1960s creations as well as Mark Millar and Bryan Hitch’s more recent The Ultimates, the script somehow manages to retain both the essence of the comics and the key aspects of the previous Marvel feature outings, which is quite an achievement.

With only one feature film – 2005’s Serenity - under his belt, some may have worried about Whedon’s relative directorial inexperience. While that film certainly had its moments, it felt more like an extended episode of Firefly than a soaring sci-fi spectacle. But much like fellow small-screen legend J.J. Abrams stepped up his game big-time from Mission: Impossible III to Star Trek, Whedon too has proven himself a remarkably more capable director here, delivering clear and coherent action sequences, impressively tight pacing, and ensuring top-notch technical contributions across the board, from the Bond-esque production design to Seamus McGarvey’s competent cinematography to Alan Silvestri’s pretty great score (aided by the London Symphony Orchestra). In fact, the Star Trek comparison is apt, because The Avengers is one of the most all-round satisfying blockbusters we’ve seen since then – displaying a similar knack for blending great action, humour and visuals with a strong story that honours its history – easily besting last year’s action highlights, Rise of the Planet of the Apes and Mission: Impossible – Ghost Protocol.

The Avengers‘ clamorous, epic final thirty-minute battle is the kind of scenario viewers have seen before in the likes of Transformers: Dark of the Moon, where an invading alien force causes catastrophic destruction to a major metropolis (here, it’s New York City). Whedon makes this familiar climax more coherent and exciting by peppering the sequences with both much-needed character interactions and snappy humour. Because we are invested in the characters, the action feels so much more tense and vital, even if the largely unexplained Chitauri invaders are merely just faceless villains for our heroes to destroy. If the glut of superhero films over the last decade has taught us one thing, it’s that a great villain is essential to make a great film. Marvel have only really got this right once so far, with Hugo Weaving’s scene-stealing Red Skull in Captain America, and here they get it mostly right. As an apparent immortal, armed with a powerful energy source and some convenient galactic allies, Loki makes a formidable foe for the Avengers’ origin story as a team, and Hiddleston – recalling a young Richard E. Grant – is once again terrific as the Norse menace. However, the film could have done with a few more scenes to explain who the Chitauri are and what Loki’s relationship to them is, and a brief recap on his and Thor’s backstory wouldn’t have hurt for viewers who missed Thor since the events of that film influence The Avengers more directly than any other Marvel feature.

Did I mention how fun this film is? For my money it’s the most fun you’ll have at the movies this year, and whether you grew up on Marvel lore or not, The Avengers should satisfy the inner child in everyone. As serious as the stakes get, Whedon is never afraid to throw in a joke – the final action sequence has one or two gags which are at least as funny as anything I’ve seen in a comedy lately – which gives the film a light, jovial tone that makes it a pleasure to watch as its brisk 143 minutes fly by. Perhaps it should be noted that The Avengers is only a superhero movie at the end of the day, and it never aspires to be anything more realistic or resonant (such as Christopher Nolan’s more highbrow Dark Knight films), but rather embraces the source material’s alternate universe of spectacle and fantasy with aplomb. Which, as Tom Hiddleston recently pointed out to The Guardian, is certainly nothing to scoff at since “superhero films present a unique canvas upon which our shared hopes, dreams and apocalyptic nightmares can be projected and played out.”

Quite simply, I am in awe of what Joss Whedon and Marvel have achieved with The Avengers - an improbable juggling act which overcomes its flaws and unwieldy nature with an abundance of thrilling action sequences, intelligent humour, a remarkably economical script, relentless energy and imagination, and some stellar performances from its talented ensemble cast. As much as I admire X2, Spider-Man 2 and Iron Man, The Avengers sets a new standard for Marvel adaptations and ranks as one of the greatest superhero films yet.

RATING: A

Note: By now fans should know to expect an obligatory post-credits scene, which sets things up nicely for Phase 2 of Marvel’s master plan (kicking off with Iron Man 3 next year).

The Avengers (billed as Marvel Avengers Assemble in the UK) is out now worldwide, except in the US where it opens May 4. Watch the latest trailer below.