Ben Stiller stars as a misanthropic ex-musician in writer-director Noah Baumbach's comedy/drama Greenberg. (Alliance Films)

Take Ben Stiller as a cranky, Zoloft-popping misanthrope who habitually sabotages his chances at happiness and success. Add indie goddess Greta Gerwig as an aimless sad sack who schlumps about in shapeless sweaters and sings rambling folk songs. Put them in a smog-wreathed L.A. and bring them together over a sick dog.

Greenberg is so determinedly downbeat that it ends up having the opposite effect. Who would have thought a film about midlife malaise could be so invigorating?

The result is Noah Baumbach’s smart, sly Greenberg, a comedy so determinedly downbeat that it ends up having the opposite effect. Who would have thought that a film about midlife malaise could be so invigorating?

I know not everyone will be charmed by Greenberg. Baumbach’s near-scientific fascination with egregious behaviour and social ineptitude have won him at least as many detractors as followers. The writer-director’s previous two films, The Squid and the Whale and Margot at the Wedding, put him right up there with Neil LaBute when it comes to serving pain-spiked comedy/dramas that have you cringing as much as laughing.

Greenberg is, by Baumbach’s standards, low-key. Sure, the title character is foolish and cruel, but he’s not in a league with Nicole Kidman’s savagely candid Margot. And, unlike Jeff Daniels’s dangerously self-absorbed writer-father character in The Squid and the Whale, Roger Greenberg mostly hurts himself. He’s never lived down the fact that, as a young musician, he ruined his band’s only shot at the big time by rejecting a recording contract for niggling reasons. That one faux pas still hangs like an albatross around his neck.

Now 40 and recently recovered from a nervous breakdown, Greenberg (Stiller) has been lured from New York, his longtime home, back to his native Los Angeles, to housesit his brother’s spread in the Hollywood Hills. Phillip (Chris Messina), a hotelier, has taken his family on a working vacation to Vietnam, leaving his hapless sibling with the house, pool and a German shepherd named Mahler. A wary Phillip has also asked his personal assistant, Florence (Gerwig), to keep an eye on things.

Like Greenberg, Florence’s life is in a holding pattern. At 25, she’s a struggling singer-songwriter who can barely afford her tiny Culver City apartment and needs her PA gig to get by. Despite their age gap, some kind of losers’ mutual attraction pulls her and Greenberg together — that and the fact that Greenberg doesn’t drive, a major handicap in L.A. He has to rely on Florence’s wheels, especially after Mahler becomes mysteriously ill and needs a vet. Still, we’re not at all sure these two misfits are right for each other. He’s chronically rude and insensitive, while she has a gift for stumbling into bad situations.

But this is not just some slackers’ rom-com. Greenberg’s return to L.A. is also a prickly confrontation with his past, as he reconnects with old friends and lovers. Among the former is Ivan (Rhys Ifans), who was the sexy British guitarist for their ill-fated band. Now an ex-drug addict who works as a computer technician, Ivan has made peace with his lot in life and shows admirable tolerance for Greenberg’s neuroses. Played with delicacy by a lanky, scruffy Ifans, he’s a sweet-natured soul whose greatest agony is his estrangement from his wife and young son.

Greenberg has a more difficult reunion with Beth (Jennifer Jason Leigh), an old girlfriend he still carries a torch for. Their catch-up lunch is one of the movie’s most poignant scenes, as it becomes clear Beth barely remembers a relationship that meant so much to Greenberg — in fact, he still recalls every detail. Leigh — who is Baumbach’s wife and co-writer on this film — turns in a perfectly calibrated performance. She’s like L.A. incarnate, with her asphalt-flat voice and chilled-out personality, betraying just a hint of anxiousness as she tries to flag a waitress and put an end to their uneasy meeting.

Florence (Greta Gerwig, left) and Ivan (Rhys Ifans) help Stiller's Greenberg celebrate his birthday. (Alliance Films)

The film is a triumph for Stiller. The man has made a very lucrative career portraying irritable, humiliated losers, but generally in the service of high-grossing, low-denominator slapstick comedies. With the role of Greenberg, those qualities become a source of sadness. Greenberg may look like an arrested adolescent, but he has the impotent anger of someone twice his age. He spends his spare time scribbling letters of complaint to the likes of Starbucks and American Airlines, like some crabby old man. (Actually, he's like Frank Constanza, the perpetually aggrieved character played by Stiller’s dad Jerry on Seinfeld.)

Greenberg is also a sort of 21st-century version of Woody Allen’s Alvy Singer, the anhedonic New York Jew out of his element in La-La Land. Not only can he not drive, he can’t swim, either, and he refuses to doff his down vest in the Southern California heat.

And if Greenberg is a Gen-X Alvy, then Gerwig’s Florence, with her endearing awkwardness and wonky wardrobe, is his emo Annie Hall. Gerwig, previously known only as a star of no-budget “mumblecore” indies like Hannah Takes the Stairs, is a revelation. Looking like a younger, American Kate Winslet, she has a warm, frowzy beauty, and she brings the loose-limbed mumblecore sensibility to her performance. She tempers Florence’s lost-girl pathos with a goofiness that’s pleasantly disarming. Getting blind drunk alone in her apartment, she sings along to, of all things, Paul McCartney’s jokey Uncle Albert/Admiral Halsey. How can you not love her?

When Greenberg acts the goof, he’s not lovable, just pitiable. The film reaches a funny/excruciating climax after he unwisely decides to party with a house full of 20-year-olds. At that point, he becomes every middle-aged person who ever thought he could relive his salad days by snorting a line of coke and slapping on some Duran Duran. We’re embarrassed, not just for Greenberg, but for our whole clinging-to-youth culture and how ultimately foolish it is.

By then, the sympathy behind Baumbach’s astringent humour starts poking through. Despite its miserable characters and grubby vision of L.A. (deftly shot by Harris Savides), Greenberg isn’t a downer. It’s a wise, even affectionate portrait of human frailty that leaves you with a good buzz.

Greenberg opens in Calgary, Edmonton, Montreal, Ottawa, Toronto and Vancouver on March 26.

Martin Morrow writes about the arts for CBC News.