In perhaps the most inspired scene in “The Secret Life of Walter Mitty,” the formerly risk-avoiding Walter finds himself in Greenland, making the last-second decision to hop onto a helicopter piloted by a giant lout of a man who has just consumed multiple mega-glasses of beer after singing in the world’s most depressing karaoke bar.

This is Walter’s reality. This is really happening. But as Walter races to the helicopter, he gains courage from imagining his co-worker Cheryl Melhoff (Kristen Wiig) strumming a guitar and singing David Bowie’s “Space Oddity” to urge him on.

It’s a questionable musical choice given what eventually happens to Major Tom (“your circuit’s dead, there’s something wrong”), but still. What’s cool about the scene is it combines Walter’s fantasy life with Walter’s real life, which is fast becoming more outrageous than his wildish dreams.

Unfortunately, “The Secret Life of Walter Mitty” rarely strives for those types of quirk-ball moments. Instead, most of Walter’s fantasies are loud, computer-generated imagery-dominated action scenes you’d half expect to see in an “Avengers” movies, while Walter’s parallel real-life quest seems, well, kind of dopey.

More than 65 years after Danny Kaye starred in a movie loosely based on James Thurber’s short story about “The Secret Life of Walter Mitty,” Stiller directs himself as the title character in a very different interpretation. This is an ambitious and sometimes effective but wildly uneven adventure that plays like one extended ego trip for Stiller. It feels like a movie by focus group, struggling to find a place between genuinely creative fantasy and audience-pleasing payoff moments.

In this version of the story, Walter is a genial daydreamer who works as a photo editor — actually they call him a “negative assets manager” — for Life magazine, which is going the way of nearly all the great news magazines of the 20th century, i.e., transitioning to an all-digital version, which means downsizing.

Adam Scott, normally comedic gold, overplays it as Ted Hendricks, a weirdly bearded, stereotypical corporate hatchet man who delights in taunting Walter and relishes in making cuts to the staff. Walter imagines a wild fight scene with Ted involving a Stretch Armstrong toy. It seems to go on forever, and not in a good way.

As his workplace life is falling to pieces, Walter stays in contact with a counselor with (PRODUCT PLACEMENT ALERT!) eHarmony (the always welcome Patton Oswalt), who takes a liking to Walter and points out it would help if Walter actually had some life experiences to put on his profile. Walter’s also crushing on that lovely and sweet co-worker Cheryl, who recently has split from her husband and has a son who loves skateboarding. (What a coincidence, Walter was once a champion skateboarder until he stopped taking risks.)

Desperate to track down a missing picture for the magazine’s final print issue — a slide said to be “the quintessence of Life magazine” — Walter journeys from Greenland to Iceland to Afghanistan in search of the legendary and reclusive photojournalist Sean O’Connell, played by Sean Penn. It was Sean who took the photo and it’s Sean who can help Walter recover it. (Sean doesn’t believe in digital photography.)

Whether Walter’s adventures are in his imagination or quite real, they’re not exciting. Sure, the CGI is pretty nifty and, as always, Stiller throws himself into the role. Of course Walter’s a superhero in his fantasies — but he seems pretty sure of himself when he’s showing Cheryl’s son some skateboard moves in New York City or dealing with menacing warlords half a world away. Where’s the evolution of character?

Stiller also doesn’t do himself any favors by having one character say Walter looks “like Indiana Jones became the lead singer of the Strokes.” That’s a cringe-inducing ego stroke of a line. (One of the big plot payoffs near the very end is even more self-aggrandizing.)

Ben Stiller’s a tremendously talented guy, and he’s directed some interesting films, from the underrated “The Cable Guy” to “Reality Bites” to “Tropic Thunder.” But he goes for big, predictable, easy and obvious too often here. Maybe in the hands of a Terry Gilliam or a Wes Anderson, “Walter Mitty” would have soared, but save for a few moments of inspired lunacy, neither Walter’s secret life nor his real life is worth your own perilous journey through the holiday crowds to the multiplex ticket window.

Email: rroeper@suntimes.com

Twitter: @richardroeper