Yeap, in fact you have to walk Paris, now, try Le Marais, this is quite an interesting neighborhood with cafés , shops and galerias... also, go to Montmartre, where the Sacre Coeur church is and walk around the village, eat a Grand Marnier crepe and watch Paris from the heights, then go for an Onion Soup where the artists are in the pintoresque square, the Salvador Dali museum is there, is not big and it is an awsome place. Walk in Saint Honoré street where all the chic boutiques are... Try eating dinner at the famous Buddah Bar... and yes, try Les Bateaux Mouches, but specially the one that is like a Bus, it drops you wherever you like and you can take it again in another stop.. you will experience Le Seine, plus you will see the top spots... another one is Saint Michel, in front of Notre Dame, the Quartier Latin is there and it is a pedestrian neighborhood full of funky restaurants from Greece, Turkey, Italy, etc...
Regarding the Louvre, after seeing the must-sees, go the other way and see the HUGE LIONS WITH WINGS from the Mesopotamian Gallery, it is an amazing gallery and it is always empty! Treasures from old Iran, you will not believe... Also, there are the old suites for Napoleon the III, the salons, living room , dining room, and also his dorm, AMAZING, some nice jewels also are exposed there, The Louvre is not only the Mona Lisa!
I agree also that the Orsay Museum is magnificent, all the impressionists are in one same gallery and it is easy to walk around. Another museum fun to see is the MODERN ART MUSEUM GEORGES POMPIDEU, it has great art, excellent gift shop and coffee shop area... finally, if you like to shop, got to La Samaritain, is it like a big SAKS in front of the Seine and go to the roof top terrace for lunch, you will be moved by the sights...ahhh, dont forget La Concergierie, where Marie Antoinette spend her last days, there is a great tour to the dungeons and the building is magnificent...uff Paris has a lot to see.. i hope you have the chance to go back again and enjoy other things... good luck!