"Hit the ground running" is a wildly inadequate way to describe the superheroic mayhem that assaults the audience within the first few frames of The Avengers: Age of Ultron: There are zinging bullets, crashing vehicles, blinding snow, flying bodies, heaving muscles, fiery explosions, and swirls of technology surrounding Tony Stark (Robert Downey Jr.) inside the Iron Man suit. It's an entire Sistine Chapel ceiling's worth of activity, and when Stark utters an appropriate -- and unprintable -- summation of the chaos, Captain America (Chris Evans) responds with a comedic dart of a rejoinder that's just the right size to puncture the tension. That skillful blend of thrills and repartee continues in perfect balance for the remaining two-plus hours, as Captain America, Iron Man, Hawkeye (Jeremy Renner), Black Widow (Scarlett Johansson), the Hulk (Mark Ruffalo), and Thor (Chris Hemsworth) must deal with the blowback that ensues when Tony Stark follows through on a modest proposal. Stark argues that his robot drones, combined with his super-intelligent computer program Jarvis (voiced by Paul Bettany), can handle the job of saving the world. So why not kick back and enjoy being ordinary people for once? It's a good plan, until one of the drones is invaded by the artificial intelligence known as Ultron (voiced magnificently by James Spader in the same creepy, dulcet purr he used to convince women to spill their secrets in sex, lies, and videotape). He's programmed to prevent humanity from stirring up trouble, and since we can't seem to stop doing this, his response is to exterminate mankind. Most movie adaptations of superhero stories are about finding an angle to give the project legitimacy: make it grittier and darker (Christopher Nolan's Batman films), make it lighter and campier (Guardians of the Galaxy), strip out the extraordinariness (Hancock), ramp up the brutality (Kick-Ass), or simply expose the seams in the genre (Birdman). To do otherwise, to approach the source material as holy writ, leaves room for Watchmen-sized debacles. Writer/director Joss Whedon, on the other hand, understands the essential nature of superhero comics so clearly that he can handle it straight, no chaser. As a screenwriter, his instinct for "enter late, leave early" keeps the scenes moving along at a lively but not breakneck pace, and he knows how to give the audience the catastrophic battles they crave while still pulling back for softer, more human moments before explosion fatigue sets in. But most importantly, he knows how to speak directly to the preteen self that yearns, via superheroes, for a simpler vision of what adulthood must be like: limitless power and privilege, chaste love, and a desire to do good in a world that hasn't yet been shaded with adult ambiguity and moral frailty. The Avengers: Age of Ultron is everything a popcorn movie should be, with a little Renaissance grandeur on the side.