The Marvel movie juggernaut has been chugging along so smoothly now for so long that it was beginning to seem that it could take any old idea and turn it into a satisfying blockbuster. Eleventh-century Nordic god reimagined as hunky extraterrestrial? Sure. World War II pulp hero defrosted in the 21st century? Why not? When last summer’s Guardians of the Galaxy pulled off the ridiculous twofer of a talking raccoon and an ambulatory houseplant, it officially felt like Marvel Studios might be incapable of failure.

With Ant-Man, however, Marvel seems finally to have met its match. The premise—a superhero who can make himself tiny and talk to ants—was tricky enough to begin with. But the picture appears, ultimately, to have been undone less by premise than by process.

Ant-Man isn’t a bad movie so much as a highly uneven one, one that manages the principal tiny-hero challenge adequately—there are echoes throughout of every shrinking movie ever made—but stumbles in small ways with regularity. It will come as a surprise to no one who’s ever watched Paul Rudd that the star displays his customary, low-key charm in the role of Scott Lang, the well-meaning burglar who is unexpectedly recruited into Ant-Manhood. Michael Douglas is likewise solid as Hank Pym, the aging scientist who invented and formerly wore the Ant-Man costume. And the rest of the cast (including Evangeline Lilly, Corey Stoll, Bobby Canavale, and Michael Pena) generally hit their marks as well.

The basic plot, too, is eminently manageable. As it did last year (with Captain America: Winter Soldier and Guardians), Marvel has again opted to follow up a big, universe-advancing epic (this year’s was Avengers: Age of Ultron) with something lighter in tone and more peripheral to its fate-of-the-Earth megaplots. In an effort to raise money to pay his daughter’s child support, ex-con Lang is persuaded to engage in One Last Heist. But the heist, it turns out, was merely a test engineered by Pym, who needs a new Ant-Man to infiltrate his old company, whose current CEO (Stoller) is about to unleash global chaos by beginning production of his own shrinking-soldier costume, the Yellowjacket. (One can envision the ensuing arms race: the Stink Bug, the Hookworm, the Chigger…)

If that all sounds rather silly, well, it’s supposed to. At its best—and with a substantial assist from Rudd—Ant-Man embraces this inherent silliness with gusto. (Again: The protagonist zips around on a flying ant he’s named “Antony.”) But the tone of the movie varies substantially from scene to scene (there’s much unnecessarily overwrought, father-daughter melodrama), substantial gaps in logic abound, and the whole ultimately amounts to less than the sum of its parts. It’s difficult to shake the sense that the film was assembled hurriedly and somewhat haphazardly.

At its best—with a substantial assist from Rudd—Ant-Man embraces its inherent silliness with gusto.

Which, from all available evidence, is exactly what happened. Edgar Wright, the action-comedy virtuoso responsible for Shaun of the Dead and Hot Fuzz, was pegged as the film’s writer-director all the way back in 2006. And he remained in that role, through multiple delays and rewrites, until May of last year, when he abruptly announced he was pulling out over creative differences with the studio. (Yes, yes, I understand that Marvel has a brand and a continuity to maintain. But what I would give to see Wright’s Ant-Man.) Adam McKay (Anchorman, Talladega Nights) briefly entered negotiations to take over before deciding against it, and in June, just 13 months ago, Peyton Reed was announced as the new director, with McKay and Rudd reworking the script. (Reed, Lilly, and Stoll also contributed ideas.) The sensible move under the circumstances would almost certainly have been to delay the film’s release. But as we know, the unfolding Marvelverse has a schedule to keep.

And so we have Ant-Man, exactly the kind of movie one might anticipate such a process yielding. The script bears all the earmarks of last-minute tinkering by multiple hands, and the emergency director, Reed—who began his career promisingly with Bring It On and the underrated war-of-the-sexes confection Down with Love before backsliding into such lazy fare as The Break-Up and Yes Man—is not up to the task of tying it all together into a satisfying whole.

Ant-Man is by no means a complete failure, and Marvel aficionados who keep their expectations in check will find plenty to like, including an appearance by one erstwhile Avenger. But the movie is well below par for the studio. It presents Marvel with the lesson that Burns’s admonition about the “best-laid schemes o’ mice an’ men” should perhaps be extended to ants as well.