Not sure what this year will look like, but a few years ago, we were there that week. A sea of people I think is the right description. Even express lanes closed as too full, for the poplar rides, and even some I thought are not as popular. If you can get up early at least one day to do early entry, go to the most popular rides as soon as you can, as the early hours are the best time to have the lower wait times, at least the first hour or so. After that, crowds just built and built.
Make sure you make meal reservations, as we saw so many turned away, and make time to get to the restaurant, as once the parks are near to close, and well thereafter, City Walk was wall to wall people. Only time my adult kids and I held hands as a chain to get through the crowds to our restaurant after arriving by boat for dinner on Christmas Day. If I’d do it again, I’d just eat at our hotel’s restaurant.
So, like any busy time, pack your patience, enjoy some pool time if warm enough, eat off hours, and try to be early, very early and use the early entry for hotel guests at least a day or two. And make sit down places reservations. You may be able to change them if not wanting to go then. There is no money penalty if you don’t show, but be considerate and cancel as soon as you know not going.
But I will say, favorite time, as everything is open, and I love holiday decorations, and the holiday parade.