Most enjoyable are the N roads (yellow on maps) which are better than our A roads but with much less traffic.
Absolutely right, but just a tiny correction; "N" (National) roads are red, "D" roads (Departemental) are yellow on the map. The mileposts (bornes) along the road have a cap of the same colour together with the road number.
Some of the "D" roads, especially in the D9xx range are as good as the "N"s as they are often "N"s that have been downgraded. For example the N138 becomes the D938.
Just be careful on the smaller roads for warning signs saying "Gravaillons". This means the roads, or potholes, have been covered in the slippery grey chippings the French use to surface their roads. Great when it is set into the surface tar, but lethal just after it has been laid.
I'm going to France at Easter (by car) I love it there and go at least twice a year.
Have a good time.