In the 1950s, the mathematician John von Neumann coined the term "singularity", the moment at which artificial intelligence advances to a point when technology exceeds and surpasses humanity. That's the moment explored in "Avengers: Age of Ultron" -- through the medium of massive 3D punch-ups.
The second movie based on the exploits of Marvel's team of superheroes sets out its stall right from the opening frame, a dizzying, one-shot romp through a snow-covered forest, the camera swooping from one superhero to another in eye-popping 3D. And it barely takes its foot off the brake as 2 hours 20 minutes of vast futuristic sets, globe-spanning adventuring and city-smashing carnage zip by, the visuals and the sound dialled up to 11 the whole way.
In terms of cinematic spectacle, "Age of Ultron" is next-level stuff. A confrontation between Iron Man and the Hulk in particular ups the ante on the scale of what can be put on a cinema screen. You owe it to your eyeballs to see it on the biggest screen you can find.
Even the more introspective character moments are easy on the eye, like when Tony Stark and Bruce Banner do... some kind of sciencey stuff, but using 3D holographic interfaces that make "Minority Report" look like Elite on a ZX Spectrum. And there's some interesting expressionistic dream sequences, including a peek into Captain America's head that hauntingly combines a battlefield with a 1940s dancehall.
Director Joss Whedon excels at this kind of human drama anchoring the off-the-chart action and badass moments. Robert Downey Jr's Tony Stark faces the hubris of his creation; Mark Ruffalo's Bruce Banner is haunted by his dual nature as the Hulk; and Scarlett Johansson's Black Widow tries to leave behind her roots as a ruthless assassin. Heck, even Jeremy Renner as Hawkeye has stuff to do.
But with its vast cast, ever-accelerating action and cameos from the wider world of Marvel, the film has to keep doubling down in a kind of spectacle inflation as it races towards its epic conclusion. Whether you find that exhilarating or exhausting will probably hinge on how much you care about the characters.
Unlike other superpowered spectacles such as "Man of Steel", "Age of Ultron" gets you to care thanks to Whedon's signature combination of emotional drama and playful humour -- extras taking selfies with Tony Stark, superhero slapstick, that sort of thing.
But inevitably, having so many balls in the air and plates spinning means that some balls and plates drop. A major late-stage twist doesn't really land because it isn't set up enough. Captain America and Thor basically have nothing to do. And themes and ideas are introduced and dispatched before they even register, like the dangers of artificial intelligence or a subplot involving Iron Man's peacekeeping drones proving none too popular with the locals.
Annoyingly, the most menacing villain simply disappears. Andy Serkis grabs his scenes by the scruff of the neck as oily South African arms dealer Ulysses Klaw, exuding stocky menace without a trace of CGI in sight, but the film forgets about him almost as soon as he turns up. Many superhero movies suffer from a lack of compelling villains -- Loki aside, of course -- and in that department, "Age of Ultron" is a mixed bag. Terrorist organisation Hydra is played for laughs, and like the first film the sequel is full of never-ending waves of faceless minions who stir no real jeopardy, existing simply to hurl themselves en masse into our heroes' cool-looking finishing moves.
The wild cards are "the twins": Aaron Taylor-Johnson plays Quicksilver as a cocky, Adidas-wearing hood who's more fun than the version we saw in "X-Men: Days of Future Past", although his high-speed effects aren't as cool. And Elizabeth Olsen's Scarlet Witch is spooky but ill-defined, with a vague range of powers that don't quite ring true.
As the robotic lead villain, James Spader's moustache-twirling vocal work makes Ultron a charismatic personality, evoking Heath Ledger's chaotic and unpredictable Joker in "The Dark Knight". Visually Ultron is kind-of scary, but only kind-of -- he's still ultimately a CGI creation and lacks weight. And I just couldn't get past the fact that he's a robot who pulls faces.
One of the burdens of moviemaking is that because the people on screen look "real", a film has to have one foot in reality -- or at least, its own consistent sense of reality. And up until now, the individual elements of the Marvel movies have had their own internal logic: rich dude builds an exo-suit. Russian assassin. Soldier is experimented on. They all feel real, with the more out-there fripperies of the comics sanded down to make sense within their internal logic -- brightly coloured spandex becomes muted armour, for example. But the Vision is a pink android who can fly and wears a cape, marking the point the film makes the leap into out-and-out comic book nuttiness. It might just be a leap too far for the casual viewer.
All small points, of course, and this is a movie that doesn't do small. You certainly get your money's worth, whether you're a casual viewer or die-hard Marvelite. "Age of Ultron" is peak Marvel: funny and exciting and noisy and colourful and sometimes even a little bit thoughtful. With spectacular action bursting out of the cinema screen, this is one singularity to look forward to.
"Avengers: Age of Ultron" opens on 23 April in the UK and Australia, and 1 May in the US.