The really wasn't a line at the ticket counter, even during the holiday season. Long lines were to get the audio guides and pay (separate line from ordering and piling up the guides). Good option anyway as e-voucher is in my e-wallet. Excellent way to spend the afternoon in rainy Paris.
Great newish museum in a beautiful chateau. We recently went to the Picasso Museum in Barcelona, as well. The two together paint the complete picture, but if you can only go to one, this would be our recommendation. The exhibition is well done, and--unique for Paris--has descriptive information in English.