Rumors of the death of quality romantic comedy are greatly exaggerated. They're just not made in English. Romantic comedies are meant to be fun, which seems to be an element lost in the equation recently.
L'Arnacouer is essentially a heist movie, but instead of robbing banks, Romain Duris and his gang are in the business of stealing hearts. Specifically, concerned fathers and brothers hire him to break up relationships they see as unfit for their sisters/daughters. So while he is generally pretty successful in his business (providing us with lots of hilarious montage sequences showing his methods and his victims), he inevitable gets the one client who is impregnable to his charms, Vanessa Paradis, better known to us as Mrs. Johnny Depp.
His early failure is a blow to his confidence, perhaps making him a bit more vulnerable, until the inevitable happens. The movie moves in fairly predictable directions (there are certain expectations in a rom-com, after all), but what sets it apart is how much charm its leads have, and how delightful individual sequences are. There were scenes where I was sporfling with uncontrollable laughter, and others where I smiled so widely I was about to break my cheeks. Duris is funny and sexy, and his energy leaps off the screen. His sidekicks are equally charming, especially his sister's husband, who aims to be a suave heartbreaker like he is but instead comes off as a creepy stalker.
Please rush out and see this, because Hollywood is already remaking it, and they are guaranteed to ruin it (I'm not a hater of Hollywood, but they have lost their way in making sweet romantic comedies that are witty and light without being cloying and unbearable. Case in point, Kate Hudson is still hired in leading roles).