Grand Theft Auto: Paris intrigues me as the French Connection films are favorites of mine. The 70s heroin scene is full of potential. Obvious question - how are you going to get around the language barrier? Or are you not?
Possibly either subtitles or characters will speak English but with French accents.
Having (a) non-French protagonist(s) could be a solution. I really wouldn't enjoy living to Frenglish for an entire game, so you could also just have them speaking plain English. In the movie Enemy at the Gates, they all just speak English, without accents (or at least without Russian accents), but of course, that might get weird when actual English-speaking characters get involved.
Edit: Christ, it's annoying when you're writing up a new story and realize how similar it is previous games.