We will be there for a few of the same days as you. Our first day in will be the day before Thanksgiving. We expect it to be pretty busy that day. Thanksgiving day will probably be pretty nice early then increasing as the day goes on. Go early, get FP's, take a break if you are so inclined, get back for a spot to watch the parade, have fun. We are going the 21st-25th, we expect a lot of people, but the parks will be open a long time and all of the entertainment options will be available.
If you were only going to do 4 days while you were there, I would pick the 22nd and 23rd for the longer hours and all the entertainment options. Take the weekend off and visit some other sites. Go back in the 27th and 28th, less hours and entertainment, but heaps less people too. We did the week after Thanksgiving in 2010 and almost everything was a walk on all week.