A scene from 'Away We Go'

No apologies for listing the whole cast of Away We Go. Sam Mendes's highly unconventional romantic comedy, written by husband-and-wife team Dave Eggers and Vendela Vida, is character, not star, driven. It doesn't conform to Hollywood marketing requirements. It's a bemused reflection on contemporary life through the experiences of a thoroughly nice, happily-in-love, middle-class American couple, a species by now almost cinematically extinct in an era when trauma is mistaken for drama.


John Krasinski and Maya Rudolph are cast against type – he's best known for The US Office, she for Saturday Night Live – as perpetual thirtysomething students Burt and Verona, suddenly obliged to behave responsibly now they're about to become parents.


"We don't live like grown-ups," she sighs, huddled up in their poorly heated home. Verona's mixed-race parents are dead and Burt's live nearby but are not inclined to stay around to see their first grandchild: they're heading off to Europe. "Will the baby be black?" asks Burt's mother (Catherine O'Hara), vaguely curious.


So Burt and Verona set off across America visiting relatives and friends to find the best place to rear their family. Away We Go evolves as a road movie, even if most of the travel is by plane rather than car.


The format allows Mendes to deliver a series of little films within the bigger film, a sort of alternative Dr Spock or How To Prepare For Parenthood In Five Dysfunctional Lessons.


First stop is Phoenix and Verona's alcoholic, loudmouth, one-time friend Lily (Allison Janney), whose idea of sensitive mothering is to ridicule her children and long-suffering husband in public. Then to the campus in Madison, where Burt's former college friend Ellen (Maggie Gyllenhaal), now a politically correct feminist professor, maintains with her guru-like husband a home routine of smug new-age perfection. "They brought us a stroller," she protests when they arrive for dinner with the gift of a buggy for her small son. "What's wrong with that?" "I LOVE my baby," she explains, condescendingly. "Why would I want to push him away from me?"


After that, Montreal, with its laidback friendliness, seems the perfect place to settle, but as a night on the town winds down, they wonder if old friends Tom and Munch (Chris Messina and Melanie Lynskey) are really as happy as they seem. Heading to Miami, they reunite with Burt's brother (Paul Schneider), trying to cope after being abandoned by his wife. So maybe Verona's career-girl sister (Carmen Ejogo) – caught up in glowing memories of childhood in a rambling Deep South house where they used to tape oranges on to a tree at the end of the garden so that their father wouldn't be disappointed because it didn't bear fruit – offers a glimpse of their future together: perhaps growing up is best when it's not too programmed but just happens.


Away We Go is a welcome move into film-making by Eggers, a young writer (and publisher of the influential McSweeney's literary journal) who values words and finds compelling stories – much as the French new wave did – in the simple fascination of observing people talking together about everything and nothing.


Mendes, through his work in theatre, is adept at revealing character and thoughts through the nuances of dialogue but also has a visual flair that, in this case, uses America's eye-grabbing landscape – both natural and man-made – to give it bigger meaning. Mendes filmed Away We Go during a break in post-production of Revolutionary Road, a much bigger film and perhaps for that reason treated more seriously by some American critics who dismissed Away We Go as "banal" – which is to miss the point.


Away We Go is terrific fun, a wryly perceptive take on contemporary American middle-class fears and foibles, smartly scripted, engagingly performed, refreshingly mature and full of wicked little surprises. It reclaims ordinary life in all its quirks and oddities as a rewarding territory for storytelling.


Away We Go


(Sam Mendes): John Krasinski, Maya Rudolph, Jeff Daniels, Catherine O'Hara, Carmen Ejogo, Maggie Gyllenhaal, Allison Janney, Jim Gaffigan, Chris Messina, Melanie Lynskey, Paul Schneider. Running time: 98 mins


Rating: 4/5 (15A)