Here's how the story (what little there is of it) goes: Taylor (Hannah Arterton) meets and falls in love with gorgeous Italian hunk Raf (Giulio Berruti) on a sun-kissed beach in Italy. But the summer is drawing to an end, and she has to be responsible and go back to school. Three years later, when she finally graduates, Taylor returns to the same Italian village to meet her headstrong, impulsive sister Maddie (Annabel Scholey) - whereupon she learns that Maddie, on the rebound from her horrible ex Doug (Greg Wise), is due to get married in a matter of days. The twist in the tale, of course, is that Maddie is planning to marry Raf - the love of Taylor's life.
In other words, the plot, such as it is, is flimsy and contrived. The narrative staggers predictably from song to song, whether it's Taylor and Raf realising they still have feelings for each other (It Must Have Been Love), or Doug and Maddie crooning about their toxic relationship (Don't You Want Me). The characters seem to function on the basis of narrative expediency: Doug, for instance, waltzes in and out of the film, teetering dangerously between unforgivable jerk and viable love interest. Truth be told, if you're looking for depth or complexity, look away now. The film seems to operate on the blithe assumption that yet another karaoke-friendly song will sweep away the awkward writing that preceded it.
The film also falters somewhat where its cast is concerned. All of them are earnest to a fault, belting their numbers with more passion than skill. They certainly work incredibly hard at playing characters with little more complexity than a batch of paper dolls: Arterton is the textbook lovelorn but responsible girl, torn between her head and her heart, while Scholey sizzles efficiently as the bubbly Maddie. But they never really manage to give off the sheer, unmitigated joy that practically radiated from the A-list cast populating the Greek islands in Mamma Mia!. Of the supporting cast, comedienne Katy Brand wins most charismatic honours as the sisters' best friend Lil - not something that can be said of X-Factor winner Leona Lewis, who should really stick to her day job.
To be fair, Walking On Sunshine does have its merits. If you're in the right mood for it, it's a silly, summery burst of fun - not quite as funny and sweet as you might want, but good enough in a pinch. Its soundtrack is great, jumping from Madonna (Holiday) to George Michael (Faith), before taking a delightful detour into tomato-strewn mayhem in the huge musical number that accompanies the title song. There are even a couple of unexpectedly rich character moments that come courtesy of the two sisters: Taylor's bravery in returning for Maddie's wedding is a surprisingly emotional moment and one of the high points of the film.
Of course, when it comes down to it, no amount of critical analysis will matter anyway. Walking On Sunshine is, quite simply, the kind of film that's largely critic-proof. It may not even be as good as Mamma Mia!, and its story and characters are almost wilfully poorly-constructed. But it won't matter because the film is also relentlessly fun, silly, sunny, and cheesy. Berruti is gorgeous to look at, as are the sun-kissed beaches of Italy. The songs are catchy, summery and joyous. That certainly doesn't add up to 'great' but, if you're open to it, it just might add up to 'good enough'.