The Brookings institute has an interesting paper on French counter terrorism:
In short, in 1980, French authorities could not even identify a foreign terrorist attack in the middle of Paris after it had happened. In 1999, they possessed a detailed understanding of a terrorist cell in another country plotting attacks against yet a third country. This striking contrast reflects a more general increase in the French capacity to prevent and fight terrorism, both at home and abroad.
As heard on NPR.
It seems the unique merging of the Judiciary and the Intelligence community in France is a significant factor in their success in preventing terrorism. Of course, the French have also had some historical problems with Islam that other countries are dealing with only recently.