Having tried a lot of french tacos in Paris, Lille & Lyon (approximately one per week), famous brands and local ones, I can definitely tell you that: I found that most taste like sht. By most, I mean 95%. Most taste like bricks of "food", without any distinctive taste, are very dry (the different sauces are sucked by french fries) BUT you will feel completely full. Not fast-food full, I used the word brick and it's the most appropriate IMHO. I tried a lot of restaurants, a lot of combinations, and I just gave up of this kind of food. And if you really like this kind of food, please try the best burrito of Lyon from Taco Taco. Das good sht.
I hope you'll prove me wrong and you'll point me to good french tacos. I'm fed up trying to find a good one :)