To be honest there is many midsize cities are unknow in France.
Nancy
Tours
Clermont Ferrand
Valenciennes
Calais
Limoges
Poitiers
Brest
Valence
Metz
etc...
France is a big country (European view) and it is really diverse in architecture, landscape and population. The most diverse in Europe.
There is a big difference between Nice and its mediterranian style and Lille and its northern industrial style.