Free Adminission to Paris Museums

The closer you get there to opening time, the shorter the lines to get in. We went to the Quai Branley Museum. There were a lot of people, but not nearly as many as at a blockbuster art exhibit or in the Mona Lisa room.

Yes, and yes and no. A few years ago I walked into the Cluny museum at opening time on free Sunday. No crowd. When I left an hour later there were many people trying to get in. I saw at other museums that there were crowds waiting to enter later in the morning, then by mid-afternoon the crowds were gone. Go early or late and you may miss the crowds.

Yes to the first (many, many times) and depends on the time of year and what museum on the 2nd question. Louvre is a nightmare and IMO it is worth it to pay for the admission another day. (And I used the carousel entrance and avoided the hours-long line for pyramid entrance). Orsay is quite crowded, line is long (but there's a separate entrance for families with young kids) and I'm borderline on whether I'd recommend paying an entrance fee another day for a smaller crowd. Smaller museums like the Cluny and Orangerie don't attract quite the crowds. And the big, open spaces of the Pompidou help alleviate that crowded feeling.

Yes! DON'T DO IT! I thought I was so smart planning the Lourve on free Sunday when we were there. We got there 5 minutes after it opened and the line was a 3 hour wait! We didn't have it in us on day 16 of a 17 day trip, so we didn't go. We did not do the Lourve when were were in Paris! One of the few big disappointments. I wish I would have just paid and went another day.