Ben Stiller has made no secret of the fact that he has high hopes for The Secret Life of Walter Mitty. In June 2012, The New Yorker ran a profile of Stiller in which writer Tad Friend followed the director-star while making the film, an adaptation of the James Thurber short story. The article made it clear that Stiller, who’s had hits directing broader comedies such as Zoolander and Tropic Thunder, wanted to go for something more seriocomic and thoughtful in tone. He further solidified those aspirations this past summer by taking the rather unconventional step of sending out letters to the press explaining his ambitions for Mitty. “I hope it is funny and serious, epic and intimate, realistic while also being sort of a fantasy too,” he wrote.

Stiller’s The Secret Life of Walter Mitty is, indeed, all of those things—but not compellingly enough. It does lots of small things right but stumbles on the grand ideas that are meant to tie it all together. There’s a pleasure in watching Stiller try for something so bold—this is easily his most emotionally complex effort since Reality Bites—but one can’t escape the movie’s overly calculated attempt to be a big, comfy crowd-pleaser at the same time. It’s a movie about individuality that feels a tad impersonal.

The second film adaptation of Walter Mitty—the first was in 1947 and starred Danny Kaye—this new version stars Stiller as Walter, a photo editor at Life whose humdrum existence is supplemented by a rich fantasy life. (Some of these are shown with the kind of scale and budget you’d expect from a summer studio tentpole, complete with action sequences.) His mother (Shirley MacLaine) is ailing, and some new executives, headed by Adam Scott’s insufferably smug Ted, have purchased the iconic magazine and decided to shut down the print edition. But shy Walter has a ray of hope in his world thanks to a pretty coworker named Cheryl (Kristen Wiig) whom he imagines whisking away in one of his many daydreams.

Thurber’s original 1939 story was only a few pages long, so Stiller and screenwriter Steven Conrad have to invent a feature-length plot. What they’ve concocted disappoints. One of Walter’s favorite Life photographers, Sean O’Connell (a nicely subdued and Zen-like Sean Penn), has sent in a roll of film that includes the mystery image that will be the cover for the final print edition—except it’s missing from the roll. Meek Walter summons up the courage to go on a potentially dangerous globetrotting expedition in search of the reclusive Sean, and so we have a road movie that doubles as a personal journey.

It’s not that this storyline is inherently unworkable—it’s simply that Stiller can only do so much with it. In the almost 75 years since Thurber’s story was published, we’ve had plenty of films, everything from Brazil to The Purple Rose of Cairo, that have expressed the sometimes poignant divide between our drab realities and our lively inner worlds. In addition, as depicted in this Walter Mitty, Walter’s voyage of self-discovery isn’t particularly novel. What’s cruelly ironic about a movie featuring an intentionally unexceptional protagonist is that Walter isn’t unmemorable in a memorable way: Stiller doesn’t play him enough as either a comic punching bag or a touching everyman to speak to us.

As a complement to a familiar storyline, Stiller injects the proceedings with a searching, bighearted spirit—with a sense of curiosity about the range of lives on this planet. Walter’s quest to track down Sean leads him to Iceland, and in the process The Secret Life of Walter Mitty becomes the sort of film that instantly equates gorgeous landscapes with an elevated spiritual core, as if all we have to do to reconnect with our true selves is to get out of the city and climb a tree. But it’s a credit to Stiller that his corniness has a real grandeur and sincerity to it. We may roll our eyes at some of Walter’s life-affirming lessons learned—one wonders how the younger Stiller of The Ben Stiller Show would have parodied this sort of mawkish Hollywood holiday entertainment—but as a filmmaker Stiller embraces that sentimentality with gusto and skill.

But in keeping with a film that wants to be all things at once—broadly comic, quietly moving, sweetly romantic, occasionally effects-driven rambunctious—the cast’s performances vary in quality, some actors more able to handle the tricky tonal balance than others. Wiig does some of her best film work as Cheryl, an unassuming woman who makes basic human kindness exceptionally appealing. But on the other end of the spectrum, there’s Scott, so lovable on Parks and Recreation and yet so irritatingly one-note as the jerky Ted, the film’s principal villain. As for Stiller, he uses his patented nervous energy to good effect as Walter, but unfortunately the character is all nervous energy. No doubt the actor-director hopes our accumulated goodwill toward him as a star will help fill in some of the gaps. But Walter’s secret life rarely shines as brightly as it should. Stiller’s aspirations flood the film, leaving its hero stranded.

Tim Grierson is chief film critic for Paste. You can follow him on Twitter.

Director: Ben Stiller

Writers: Steven Conrad (screenplay); James Thurber (short story)

Starring: Ben Stiller, Kristen Wiig, Shirley MacLaine, Adam Scott, Kathryn Hahn, Sean Penn

Release Date: Dec. 25, 2013