One of my favorite museums in Paris is the Luxembourg, located at the base of the Jardin de Luxembourg at 19 rue de Vaugirard. The expositions are not at all overwhelming, as the space is relatively small. The theme, therefore, is generally very sharply focused, making it quite pleasurable to savor and understand the art in the intimate space there. Of course, it's also lovely to take a stroll in the garden afterwards.
The image of the angel above is a study of a Véronèse painting from a show I saw at the Musée de Luxembourg some years ago, called Véronèse Profane.