After skewering suburban bliss in the blackly comic American Beauty and the bleakly tragic Revolutionary Road, Sam Mendes takes to the highway for this slight, but engagingly quirky, indie-lite road movie.

This time, his rootless thirtysomething middle-class couple criss-cross North America seeking the perfect friend-and-family-filled spot to raise their baby. John Krasinski’s goofy Burt agonises adorably with lady love Verona (Maya Rudolph) while Alexi Murdoch’s songs provide warbling wallpaper. Factor in the pootling pace and subdued palate, and all seems quiet. Too quiet. Is this some alterna-world where Mendes makes mumblecore?

Nope, the movie’s just idling cutely before unveiling some of Sam’s unhappy families. From Phoenix to Florida, Burt and Verona’s hosts run the gamut from grotesque (Allison Janney going OTT as a loopy loudmouth mom) to grimly unhappy, as a picture-perfect Montreal household unpeels to reveal agonised infertility.

Among them, there’s the odd delicious vignette, like the stopover with ‘cousin’ Ellen (Maggie Gyllenhaal), a preening, patronising New Ager who indignantly refuses the gift of a stroller (“I love my babies. Why would I want to push them away from me?”). Mendes’ characteristic sad/sour notes surface too, as Verona mourns her long-dead parents and a suburban husband vilifies an America he despises.

The script, by married literary duo Dave Eggers and Vendela Vida, is undeniably insightful about the anxieties of first-time parenthood. Yet the movie only seems to have one speed – leisurely – and two moods, snarky or sweet. It’s down to the performers to provide the nuances, with uneven results: witness caricatures like Catherine O’Hara’s shriekingly selfish mother-in-law (“How black will the baby be?”), who more properly belongs in a Christopher Guest movie.

Still, Krasinski and Rudolph bring a low-key playfulness to Burt and Verona’s tender interludes, and to their fretful inability to live proper, grown-up lives. Rudolph, tough and fragile all at once, is a particular delight. But even she can’t compensate for the film’s dawdling, episodic quality and a certain smart-mouthed smugness throughout.

It’s hard to love a movie whose central couple are so self-involved that even when Burt’s sister-in-law deserts her daughter, it’s just a peg on which to hang their own Gen Y angst about parenting. And then there’s the feel-good wrap-up, cornier than Kansas in August. So perhaps Mendes hasn’t strayed far from the mainstream after all.

Underneath Away We Go’s hip, indie trappings and starry cameos lies yet another Noughties ‘we’re not ready for a baby’ comedy. And we really needed another one of those.

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