Boy, did that shot of the Mona Lisa bring back memories.
DH and I went to Paris in 2013 and never got near the Mona Lisa or the Venus de Milo. Not worth it, in our opinions. We didn't like the d'Orsay, either. were pretty much routed along a wall, behind people with iPads who would stop, take a photo of the painting, take a photo of the information panel, move on... that's not how to experience Impressionist paintings. One way is to start at the wall, but then back up and watch the picture emerge from the brush strokes. Impossible given the crowds. Fortunately I'd seen a podcast featuring an exhibit of Slovenian Impressionist paintings at a smaller museum (Le Petit Palais)- who knew there were Slovenian Impressionists?. We went over there and there were very few other tourists. It was wonderful. I was in Paris for a couple of days last October and mostly wandered. Beautiful weather, interesting architecture, people-watching. I loved it even though I missed the "must-see" spots.
I know that, being a tourist, I'm part of the horde so I can't complain- but from now on my tactic in the overcrowded areas will be to find the lesser-known museums, the less- traveled cities for day trips, etc. There's still plenty to see without standing in line.