One of three museums within about 500m, the Nissim de Camondo is, to me, the best in terms of the overall experience. It is (was) a family home, like the other two (Musée Cernuschi, Musée Jaquemart-Andre), but this one has a more of a 'lived-in' feel, in that you see bathrooms, kitchens and get more of a feel for how the household functioned.
But really, it is all about the architecture and the paintings, tapestries, ceramics, sculpture, and furniture. It is the house of an avid and dedicated collector with deep pockets... who sadly had no heirs and like the other two museums, left the house and collection to the nation.
Audioguide is included in the price, entrance fee is €9, open 10:00 to 17:30, closed Mon. and Tue. Metro Monceau or Villiers. Stairs aplenty, and no elevator.
Depending on your stamina, the other two mentioned (reviewed separately) could be done in one full day, with perhaps 30 minutes on a shady bench in adjacent Parc Monceau to recharge the batteries in your lunch break!