The opening scenes of While We're Young are peppered with a suite of hilarious, rapier-like exchanges that plunge you into 40-something-year old couple Josh (Ben Stiller) and Cornelia Srebnick's (Naomi Watts) limbo. Strained by the seemingly sisyphean struggle of finishing a documentary he's spent almost a decade making and recovering from the trauma of multiple miscarriages, they lack direction and have become detached from one another. However, when enthusiastic young filmmaker Jamie (Adam Driver) and his ice cream-making wife Darby (Amanda Seyfried) turn up at one of Stiller's filmmaking lecturers, the characters start to move.

This is a rite of passage film for an underrepresented group, but not an underprivileged one: should we care about upper middle class folks in their mid-forties? Director Noah Baumbach's search for sincerity mirrors that of his protagonist, and this symbiotic plight commands your concern. Through the eyes of their best friends - 'regular' couple Adam Horovitz and Maria Dizzia - we're able to take a seat with the Greek Chorus and glare in bemusement at their trilbies, hip-hop dancing and struggles.

Cornelia and Josh's adulation of the young couple is so entertainingly shallow ("I love his shoes", "his taste is so democratic") that it's very difficult to navigate your way through the blind spots. By the time you've made your way past their projections, you struggle to interpret the hang-ups of youth with jaded eyes and arthritic fingers. Your vague understanding of the young couple is perpetuated by Baumbach's uncharacteristic yet intentional use of montage to haphazardly stitch the characters together. Even when Driver, a man who is becoming increasingly dominating every time he appears in a picture, smacks Watts in the face with the drug-infused line "I don't think I'll never die," it's hard to disagree with him. He's spent the past forty minutes convincing you of it too.

In While We're Young, Baumbach's sharp riposte adds texture to the progressive use of dialogue that we've seen in his filmmaking over the past decade. In this instance, we're jabbed by one-liners with one hand whilst the situation is moulded into something more contorted and ridiculous with the other. In the scene where they take Mexican hallucinogens, you have a group of bare-footed support group hippies trying to wrestle their visions of Egyptian imagery between casually throwing up into a paper bag. Down to esteemed filmmaker and Father-In-Law Leslie (Charles Grodin), the delivery throughout is perfect. The casting has been an integral part in Baumbach making the funniest film he's ever written.

Seemingly revitalised by the young couple, Josh and Cornelia uncharacteristically hand themselves over. As they volunteer themselves to help finish and fund Jamie's film in a slapdash fashion, allowing him access to a 'once in a lifetime' expert and unknowingly giving him the opportunity to meet Cornelia's wealthy father Leslie, the seams of cynicism begin to show. By the time that Josh cries 'eureka', we're losing our voices from yelling it. Embroiled in Josh's irrationalities, we cheer him on as he speeds into the home straight. The film's defining shtick and climax has you so caught up that the giant slap around his face stings you as much as it does he.

Despite being disillusioned to begin with, Josh's strive for truth is central; it's the reason why he can't finish his film "about America". However, this pontificating brings him closer to Jamie and, as their relationship intensifies, he loses sight of what exact truth he's searching for. Only in the light of betrayal is he able to become self-actualised and, driven by the struggle for truth in the world again, he can finish his film and move on with his life. Jamie and Cornelia emerge as the unlikely victors in a friendship completely built on the abuse of one another.