For about a decade now, I’ve been part of a super-secret cabal of movie nerds. When we’re not discussing specific films, the conversation often turns to more general notions—for example, the theory of the “interesting failure.” This is the postulate that certain risk-taking works may be laudable simply by virtue of their risk-taking-ness—in sports metaphor terms, that the degree of difficulty of a dive should count for a lot, even if the diver lands ass-first in the middle of the pool.

Usually, such conversations revolve around artsy experiments like Richard Kelly’s Southland Tales or David Lynch’s Inland Empire—nothing remotely like Hancock, a big-budget summer superhero blockbuster starring Will Smith. But it may be time to tweak our definitions, because I can’t remember a recent mainstream film that deserved the “interesting failure” designation more.

The concept that the ads have been selling is pure high-concept action-comedy: Patrolling the streets and skies of Los Angeles is a Hancock (Smith), a stubble-faced, alcoholic, short-tempered, misanthropic douchebag of an indestructible superhero. While he leaps to the bourbon-soaked rescue when criminals are plowing through the freeways, he generally leaves a wake of indiscriminate destruction and pissed-off bystanders. But one of Hancock’s rescue-ees—freelance publicist Ray Embrey (Jason Bateman)—thinks he can rehabilitate Hancock’s image. So it’s off to voluntary incarceration for Hancock on his many failure-to-appear warrants, where he can straighten up while waiting for the city to realize it needs him.

And oh, the potential hilarity built into that set-up. You’ve got the sheer mayhem that can be caused by an all-powerful dude with his drunk on, like slinging a carload of bad guys onto the spire of the Capitol Records building. You’ve got the prospect of a superhero in jail, forced to fraternize with the hard-cases he put there and struggle through group therapy. And you’ve got Bateman—who has become one of our truly great deadpan comedians—trying to make a Spandex-clad purse out of a pig’s nether regions, all in the name of trying to change the world for the better.

It all comes together for a lively and entertaining first half, with the occasional obvious and unnecessary detour into an over-the-top visual gag. But something’s always bubbling beneath the surface, something that’s instantly apparent when Ray brings Hancock home to meet the family and his wife Mary (Charlize Theron) shifts her eyes in an embarrassingly obvious “I’m about to become part of this guy’s back-story” way. With the initial character arc apparently resolved in around 40 minutes, we learn that Hancock’s “issues” stem from an unresolved case of amnesia, and that he hasn’t aged for (at least) 80 years. What would you do if you were going to live alone, forever, compelled to do good but with no idea why?

That’s the high-degree-of-difficulty idea director Peter Berg (The Kingdom) and screenwriters Vincent Ngo and Vince Gilligan spin out of that high-concept opening—and who knows, maybe it might even have worked. But as more and more of Hancock’s history is revealed, the film starts to drift from its lighter tone into something dark and ominous. The filmmakers waste time on the machinations of a vengeance-minded crook (Eddie Marsan), building to a climax that’s brutally melodramatic—and that’s “brutal” both in the “violent” and “pretty terrible” senses of the word.

Perhaps it all might have felt more worthwhile if Hancock didn’t shortchange nearly every issue and character motivation it raises; there are more than enough missing story beats to flesh out the movie’s 80-some-odd minutes to 105 or so. The upbeat coda proves particularly galling, turning the plot’s emotional pivot point into a wacky punch line. At times Hancock wants to be more than “fun,” and perhaps that’s to be admired. But by the time the credits roll, it’s less about the twists it makes in the air, and all about the dull smack as it hits the water.

HANCOCK

** (two out of four stars)

Starring: Will Smith, Charlize Theron, Jason Bateman.

Directed by Peter Berg.

Rated PG-13.