It's unseasonably warm and we've only just got to November, but whether or not you think it arrives horrifyingly too soon, the London opening of Elf the Musical officially heralds the start of the festive season. It's time to pull out your comedy Christmas sweaters.

Based on the 2003 film starring Will Ferrell, Elf the Musical is as saccharine as a full box of Quality Street. Buddy thinks he's just another one of Santa's elves up in the North Pole, oblivious to the fact that he's as tall as at least two of the tiny toy makers. When he finds out that he's actually human and his father is in New York, he heads out into the big bad world to find him.

It's a horribly bland plot, which is pepped up by the charmingly idiotic Buddy. He is clueless about everything, except Christmas, and has an irrepressible sense of fun, magic and wonder which flies amusingly in the face of his angry businessman father.

Fans of the film will tell you Ferrell's Buddy was an absolute hoot. Here, Ben Forster is the show's saving grace. Kooky, gawky, excitable and enthusiastic, Forster taps into a similar off-beat humour that Ferrell did. He delivers the jokes for the adults with a dead-pan innocence (‘I'd love to put you on top of my Christmas tree!') and he can certainly sing. His was the voice that won Andrew Lloyd Webber's Superstar, the TV search for that other Christmas icon, Jesus. But it's the comedy that he excels at here, and which will woo even the most bah humbug of audience members.

Elsewhere, though, the show is a slog. Thomas Meehan and Bob Martin's book compresses the original into a blur of short luminous scenes – set everywhere from Santa's grotto to Macy's – which don't allow us time to get to know any of the other characters. Kimberley Walsh barely has a part as Buddy's love interest Jovie, and she's wooden with the dialogue. But she can sing, and she delivers on Matthew Sklar and Chad Beguelin's pop-friendly songs. "Never Fall In Love With An Elf" is her stand out tune and she's great. Elsewhere Joe McGann does as much as he can with another paper thin character, Buddy's father Walter Hobbs.

In general, Beguelin and Sklar's tunes are surprisingly forgettable, although "Nobody Cares About Santa" and "Just Like Him" are both nicely snappy. Tim Goodchild's designs offer some surprises, and thankfully don't go all out glitter and snow globe, often relying on Ian William Galloway's video projections to set the scene.

So, let's not be a Scrooge about it: Elf the Musical is no perfect snowflake, but, thanks to a strong turn from Forster it's not a total turkey either.

Elf the Musical is at the Dominion Theatre until 2 Jan.