Whatever other accusations you may wish to throw her way, you could never complain that Zooey Deschanel wilfully confounds her audience's expectations by playing against type. The critics may have tired of the on-screen persona characterised by one of their number as Manic Pixie Dream Girl ("adorkable or tweepulsive?" pondered Vanity Fair of her latest vehicle, the sitcom New Girl; the Onion simply retitled the show Zooey Deschanel's Nerd Glasses and Quirky Sense of Humour Render Her Undateable), but on she doggedly ploughs, or rather skips. Over on the website she co-founded, hellogiggles.com – recent posts include Thank You for Being My Cat, Winnie the Pooh Is a Friend of All of Ours, and Ponies – her latest missive furnishes a grateful world with the information that 7 December is Bestie Day. "I have a brand new list of weird suggestions for how to use this day to appreciate your beloved bestie!" writes Deschanel, who is 31 years old. "Make her initials in pancakes. Yum!"

Anyone who feels that kind of thing might cause them to bring up their last batch of pancakes is probably best advised to give her ongoing musical career a wide berth. In fairness, She & Him, her collaboration with Portland singer-songwriter M Ward, is a little less cutesy than you might expect from a woman whose previous musical project was called If All the Stars Were Pretty Babies. That said, fans never want for photos of Deschanel pulling kooky faces while wearing vintage dresses, and their last album contained a cover of Get Along Without You Now, a song made famous in 1957 by Patience and Prudence, a singing duo consisting of two sisters aged 11 and 14. Fans of Dimmu Borgir are thus advised that She & Him's oeuvre is probably not for them: in the unlikely event that any black metal heads are still on the fence, it's worth noting that the deluxe edition of A Very She & Him Christmas comes with a free pair of mittens.

Still, if ever a genre entitled its practitioners to dabble at will in toothsome cutesiness, it's Christmas music. The most deathless Christmas records tend not to be made by minimal techno auteurs or post-rock bands, but artists barely on speaking term with concepts such as subtlety and good taste: Wizzard, Slade, Elvis, Phil Spector. Oddly, however, She & Him have chosen this moment to scale back their honeyed sound. There's almost nothing to A Very She & Him Christmas: acoustic guitar, Deschanel and Ward's voices, occasional shadings of piano or reverb-heavy electric guitar.

It's all very well done – Ward is a great guitarist and arranger – but there's something audibly lacking. The idea is clearly to put a different emotional spin on the well-worn classics they cover. The influences they mention – the Carpenters, the Beach Boys and jazz pianist Vince Guaraldi's peerless soundtrack to the 1965 TV special A Charlie Brown Christmas – all famously dealt in melancholy of one kind or another. But in the cases of the Carpenters and the Beach Boys, the emotional power came from the way the ineffable sadness of Karen Carpenter's voice or Brian Wilson's melodies chafed against the sumptuousness of the arrangements. Likewise, the impact of Guaraldi's score is founded in the way its emotional temperature keeps changing from hushed and contemplative to five-year-old-on-Christmas-Eve.

Here, however, almost everything seems to proceed at the same stately, tasteful pace, save for Christmas Day, which breaks out the massed harmonies and drums and feels fairly magical. Elsewhere, however, it doesn't feel melancholy so much as joyless: their versions of Rockin' Around the Christmas Tree and Baby, It's Cold Outside seem weirdly forced, as if they were performed at gunpoint. It's a state of affairs compounded by Deschanel's voice. She's certainly not a bad singer as such, but she's a weirdly expressionless one, which is a problem when the album is so stripped back. Her take on Have Yourself a Merry Little Christmas sounds like it was recorded at about teatime on 28 December, shortly after the in-laws have announced they've decided to stay until New Year.

Of course, being bored stiff is a perfectly sane and believable response to Christmas. But it doesn't really make for great Christmas music, partly because Christmas music is surely all about a certain unreality, the suspension of disbelief, and partly because boredom is contagious. Unlikely as it seems, A Very She & Him Christmas could have done with a little more of the wide-eyed, kooky-face, make-your-bestie-a-yummy-pancake Deschanel: the results might or might not have been unbearable, but they certainly wouldn't have been dull. Instead, she seems to have decided to play against type at precisely the wrong moment.