The d'Orsay museum is not as gigantic as the Louvre, but it too really needs days to appreciate.  Out of the two museums, I prefer the art in the d'Orsay.  It's really amazing seeing works of Monet, Degas, Cezanne, Renoir and Van Gough in person. The d'Orsay is particularly known for their impressionist collections.  No poster reproduction (nor our photos) can capture these master pieces.  Monet's Le Parlement seemed be glowing on the wall.We really liked the huge open atrium of the d'Orsay.  The building is actually an old railway station.  You can watch time tick away on the large clocks around the building enjoying the amazing art.