We go to Disney at that time of year every time we go.... It's a wonderful time. You might get some cold days and yucky rain, but I have found the weather to be very pleasant that time of year. We have been able to swim in 75 degree temperatures most of the trips, but it is safe to bring layers and a rain slicker just in case.
I love the Candlelight Processional and the Dinner Package included w/ it is really nice. The Osborne Light Display at MGM is wonderful to walk thru while sipping hot chocolate, but I heard on the boards this will not be open this year, but if you go again at that time in the future, I think it is a must-see. The Spectromagic parade usually runs at the MK on weekends this time of year and it is a marvelous parade all done w/ lights. The Christmas Parade is really great and if you just want to see the parade and have a great spot for it, you can go to Mickey's Very Merry Christmas Party and watch it that evening. Some of the floats are harder to see due to the darkness, but it's not that bad in visibility and it saves you the crowds. Plus,
MVMCP is a wonderful treat, if you can afford it. It is in the evening after the MK closes.... it snows on Main Street, has a Christmas Parade and Fireworks and only allows 20,000 people into the park which cuts down on the crowds considerably. And so the ride lines are a lot less as well. If you want to see the Parade during the "shooting" for Christmas Day, you must get there early and they keep stopping and starting the parade for the cameras. I enjoyed seeing Regis and Kelly and had a wonderul seat on a bench by the Main Street Christmas Tree. If you want to see the parade ON Christmas Day.... now that will be VERY busy. Get there early and sit and sit and sit until it begins.
Blizzard Beach is also fun because it is themed like a melting ski resort, appropriate for the season. Lastly, the must sees are all of the wonderful tree lighting ceremonies, the wonderful decorations (esp. the light display you walk under to get from Future World to the World Showcase in EPCOT and the fountains in Future World in EPCOT) and the skits thrown by each country in the World Showcase regarding their celebration of Christmas. Those are really neat to see. Most of these you just stumple upon, but were some of the most enjoyable moments our family had. Go the opposite way of the crowds and you'll be surprised of what you will see.
I hope you enjoy your stay! I'll be thinking of you.