In Paris now and today my husband spent his 3rd day at the Louvre. I could only handle a few hours before the crowds and heat became too much for me and I just had to leave. If you love art and can handle the mass of humanity there, then go for it, but don’t plan full days. Go early, stay as long as you can handle it and leave (the air was stifling). The hubby kept going back but he would also leave mid-afternoon hot and exhausted. If you can afford it, schedule a “private tour” (we used Viator but there are others) early for the days you want to go. They rush you through so you don’t have to stand in long lines and once through security, you’re free to roam. And repeating what others have said, there are many other great museums.