The mainstream romantic comedy genre arguably finds itself at the lowest point of its long existence, thanks to a series of rom-coms, starring the likes of Katherine Heigl and Jennifer Aniston, that prove short on comedy and equally bereft of romance. The art of storytelling seems to have been forsaken by the genre, with the same generic "when will Boy A and Girl B realise how perfect they are for each other?" plotline trotted out ceaselessly. What If serves up this tired platter once more, but while there's little in the way of romance, there is a healthy dose of comedy on offer.

The film's charm exists thanks in no small part to its talented cast. The likes of Kazan, Adam Driver, Mackenzie Davis and Spall deliver comic timing par excellence, but it's Megan Park - who this reviewer last noticed in George Romero's under-rated found footage zombie satire Diary of the Dead - who steals the show as Kazan's sexually ravenous sister, determined to sink her claws into Radcliffe, much to sis's chagrin. Radcliffe is the odd one out, however, and feels lost among such more naturally gifted comedic performers. Luckily he possesses a breezy likability that papers over the comic cracks.

The film is admirable for how sex positive it is, and it never feels like it's pouring scorn on its sexually confident female characters. In this regard it's the anti-thesis of this year's earlier risible misogyny fest That Awkward Moment. Compare the idiotic wet blanket MacKenzie Davis, one of the most promising young actors to emerge in recent years, played in that movie to the feisty tigress she portrays so well here.

Relying on the charm of its cast rather than pulling you into anything approaching a story, What If feels like a pilot for a TV comedy series. It promises much but delivers little, yet you're left wanting more from its infectious characters.