We may not need another hero, but true believers don't need to shrink-ray their expectations. Ant-Man is the first Marvel film — and the first of this summer's pixels-go-kablooey time-wasters — to get better as it goes. The filmmakers save their biggest, wiggiest ideas for the climaxes, where they wittily reduce the pageantry of destruction to HO scale: In one of many third-act dustups, our hero faces off against the latest Marvel tech-gone-wrong baddy on an architect's model of a building. (It suffers the fate of Man of Steel's Metropolis.)

From there the action flits to even more humdrum locales, intimate of-our-world spaces. This freshens up the usual superheroics. No spoilers, here, about the half-dozen surprises the filmmakers uncork in the last half-hour, but isn't it a relief that once again there are marvels to spoil? I couldn't have spoiled the action in the Thor or Avengers sequels if I had tried: Two hours in, the digital villains were still gushing at us, as if the CGI were coming from some faucet a kid had left running.

Ant-Man, by comparison, makes a virtue of drought-year scarcity. The movie favors story over set pieces, never even trying to dazzle us for a good 40 minutes — and then heading back to hang out in a San Francisco Queen Anne owned by Ant-Man mentor Hank Pym (Michael Douglas). Not that said story demanded to be told, of course: This is familiar superhero origin and training stuff, spiced with heist-planning and the comedy of dumbfoundedness. As the goodhearted burglar who winds up with the powers to shrink himself and boss ants around, Paul Rudd spends the first hour looking like neither he nor his character, Scott Lang, can buy that a guy like him could possibly be a hero. Maybe in the Marvel Cinematic Universe, the entire history of Hollywood is different?

Directed by Peyton Reed, Ant-Man is spry and often funny, despite its familiarity: Just as in Jurassic World a few weeks back, the villains here plan to militarize some priceless science-fiction tech. If not quite the loose surprise of last summer's Guardians of the Galaxy, it's blessedly free of gods-weep ponderousness. But it's also uncentered in a way that Marvel's origin films have never been. We see Lang become Ant-Man but learn too little about the more interesting man he was before that. In the first scene, the not-yet-superpowered Lang is serving time for his brilliant burglaries of tech millionaires. The film makes clear that he held to some moral code in his thieving, but doesn't bother sharing it, or how he got to be celebrity enough that his arrest made the newspapers. His criminal acumen is simply a given, like Captain America's fightin' spirit, rather than a discipline the character once set himself to master.

So Rudd has little to play. He shrugs through the long buildup, a vague everyman schnook despite his good looks and mighty abs. (Early on, in the name of product placement, he runs a register at Baskin-Robbins when he clearly could be teaching spin and core classes.) Lang's neither flip about superheroing nor especially into it — he just seems relieved to have someplace to go and look a little annoyed. To make all this seem to matter, Douglas, playing inventor-cum–life coach, has to keep speaking the hero's motivation out loud: "Redemption."

Redemption, of course, is the idea that movies without ideas always pretend to be thinking about. Here, it just means he's given the chance to perform feats of heroism in front of the family who moved on while he was incarcerated.

Douglas guides Rudd and the film through the self-help paces, teaching him to believe in himself and to boss ants around. It's mostly shot without distinction in the Marvel house style — lots of drama in steel-and-concrete laboratories, punctuated with stabs of pathos and pop culture. But that house style is effective, especially when applied to time-tested formula, and the mundanity lends power to the miracles. When we fly with Lang at last, on the wings of carpenter ants, over Coit Tower, the film has the tingle of giddy possibility of Sam Raimi's first Spider-Man.

Ant-Man ends well and is sturdily built, but there's rot at the margins. Judy Greer turns up as Lang's ex-wife and the mother of his daughter, the second time this summer this gifted actress has played a woman who worries while someone else has a blockbuster adventure. The best that can be said of all this: At least they don't make her fall back in love with him.

Evangeline Lilly plays Pym's daughter, a martial-artist corporate exec who detests Lang on sight — and, wouldn't you know, later finds much to admire. There might have been some satiric power in the fact that Lilly's Hope van Dyne yearns to be a hero while the diffident Lang is simply given the role, but the film doesn't dare take that on. It's no breakthrough that she gets to ask, repeatedly, why she can't be in the superhero suit, or that Douglas, as close to an official representative of the patriarchy as I can imagine, has to take time from Lang's adventures to address her complaints. But there is cause for encouragement: Marvel won't make a woman the lead, but the studio now feels obliged to pack its films with plot excuses as to why not.

Meanwhile, Lang's crew of merry thieves finds strong non-white actors wasted as cowardly, superstitious stereotypes. In his first scene, Michael Peña has to report that his character's father has been deported — and, since this news means little to Lang, it's treated as a laugh. If this were an old-school talking-animal Disney cartoon, Ant-Man's sidekicks would all be hyenas or something.

For non-devotees of the comic-book film, Ant-Man is decidedly a glass-half-empty situation. But fans won't care: That glass is also half-awesome, and that's enough.