We did Christmas week back in 2016, and are doing it again this year. Like everyone else said here, patience it key. Because of FPs and ADRs we were able to get on all the rides we wanted. We did a lot of resort hopping, and took in the atmosphere. It was a great time. We found that MK in particular wasn't actually that busy late at night, we assume because families with little ones were done with parks after dinner. We did actual Christmas Day at Epcot, and while busy, it was still a great time.
This year who knows what's going to happen. No FPs yet, shorter window on ADRs. Unsure hours. We have no idea what we are in for. We do know that we will enjoy it no matter what. Just being there soaking up the atmosphere is huge for us.
One fun thing we did was Xmas Eve our family (Wife, myself, and 2 daughters ages 16 and 23 then) decided to each take $100, and buy gifts for each other. You could not spend more than $100. It was a great time scavenger hunting throughout the parks and Disney Springs finding that perfect Disney something for family members. The next morning we woke up, and all the gifts were under a little tree we had brought with us in the room, wrapped in those famous blue/purple Disney bags. Lots of fun!