The Saint-Denis center point is about the area of Stade de France and the area of Saint Denis Basilica.
Below are reviews of the city of Saint-Denis, France from an actual visitor's perspective.
My stay was based upon the NFL game. So didn't see much of Saint Denis. But overall France is wonderful. Le Marais, Saint Germain and Monmartre were beautiful to visit.
Hotel is near the metro.
Nice part of Paris!