Rust and Bone, Jacques Audiard, 120 mins (15)For a Good Time, Call..., Jamie Travis, 85 mins (18)

His gritty and intense tales have won Jacques Audiard a considerable following, but for all its drama, his latest film feels fey and insubstantial

Jacques Audiard is fast becoming the world's favourite French director – and all without the help of Uggie the dog. His last two films, The Beat that my Heart Skipped and the 2009 prison drama, A Prophet, were near-flawless examples of how to revitalise a genre movie by packing it with passion, depth and distinctive, flesh-and-blood characters. His new film, Rust and Bone, also benefits from the star power of its leading lady, Marion Cotillard, so it could be his biggest hit yet.

Before we see her, though, we're introduced to Matthias Schoenaerts, a brawny, bearded, unemployed ex-boxer who takes his five-year-old son from Belgium to the Cote d'Azur, where he moves in with a sister he hasn't seen in years. After he gets a job as a nightclub bouncer, he meets Cotillard, a killer-whale trainer in a marine park. She seems to be several miles out of his league. But when she loses her lower legs in a grisly accident, his straight-talking, unpitying support is what she needs.

There's a lot about Rust and Bone that's excellent, not least its astonishing digital effects. Never mind creating Gollum or the Hulk, CGI doesn't get any more mind-boggling than when it's showing us Cotillard with nothing below her knees except thin air in some scenes and metal limbs in others. What's even more impressive is the raw intensity of Cotillard's performance. The moment when she steps out of a van, on prosthetic legs, with a look of ferocious, Lady Macbeth-like determination on her face, you know you're watching one of our most dazzlingly bright movie stars. Schoenaerts, on the other hand, is more like Tahar Rahim in A Prophet, in that he never seems like an actor playing a role, but a real person who has somehow wandered into a fictional film.

As strong as Audiard's drama is, however, it didn't affect me as much as I wanted it to, probably because its initial, harsh social realism soon goes soft. Despite all the scenes of amputation, depression, casual sex, and bare-knuckle boxing, the film can feel insubstantial, fey and just a bit too beautiful. There's always plenty going on, but none of it ever threatens to stop Cotillard and Schoenaerts getting together (assuming their relationship doesn't hinge on anyone being able to spell his surname). By the end, it's become a soppy romance about two damaged people finding love and learning to live again. There's rust and bone in there, yes, but cotton wool, too.

For a Good Time, Call ... is an indie comedy about two young women (Ari Graynor and Lauren Miller) who can't stand each other but have no choice but to share an apartment in New York, where they set up a phone-sex line and become best friends. And that's it. There aren't any other complications or subplots. Even when one of the women gets a boyfriend, and the other gets a surprise visit from her parents, any awkwardness is forgotten a minute or two later, so that Graynor and Miller can get on with hugging and declaring their love for one another.

The film's biggest mistake is to assume that phone-sex lines are so inherently scandalous and hilarious that it won't take anything more than a montage of the women talking dirty to have us rolling in the aisles. But aren't these particular services a pre-broadband phenomenon? I'm no expert, I promise, but I remember the phone-sex operators in Robert Altman's Short Cuts in 1993 and in Spike Lee's Girl 6 in 1996, so I wonder what the director's next film is going to be about – Blur and Oasis's race to get a No 1 single?