We went last News Years Eve/New Years for the first time. Had so much fun we are going back this year. First, just keep your eyes open and look around! All the parks and resorts are decorated for the holidays and are beautiful.
The things I remember:
MK: There is a great show in front of the Cinderella castle in the evenings, lots of characters, music, etc. Main street at night is great being all lit up, and one night they had real snow falling from machines on the rooftops that set a great mood. Also don't miss Wishes. This park got quite crowded (understatement) except for first thing in the morning. If you want to do the attractions in the back (Peter Pan, Snow White, Dumbo, Mickey's Philharmagic, etc) with little to no line, then get up early one morning, be at the gates 30 minutes before opening, and head straight back. We did all of these in the first hour the park was open. By 10:00 AM there are one hour plus (2 1/2 hour waits for Peter Pan?) waits for each. If you are into the parades, check the times and attend.
Epcot: We did this park for New Years Eve. Whatever park you do for NYE, plan on being in the park by 2-3:00 PM to guarantee admission. MK maybe even earlier as it seems to get the most jammed. Epcot has a christmas tree lighting ceremony at 6:00 PM that's nice. It's near the beginning of the Worlds section. Mission Space and Test Track need to be fast passed for sure. The NYE version of Illuminations is at 7:30 and again just before midnight. With kids we did the 7:30. By 7:00 it was stand-still crowded everywhere around the lake. The show was magnificent. After the show, the crowd loosened up. Keep and eye on the kids though. We had a 6:00 priority seating at Rose & Crown (England) figuring we could eat on the outdoor deck and watch the show from there. Never happened, all the earlier seatings just sat at the tables for hours until after the show. We finally got a table at 8:15. People in the line were furious! So this year we are going to do a dinner reservation earlier and finish before the show.
MGM: Again, beautiful decorations. Take in the Fantasmic show especially if you have not seen it. There are two shows a night during this stretch, and 3 shows on the 30th and 31st (that should tell you something about the crowds). The later shows will be less busy. Some of the MGM restaurants have a dinner/show priority seating for the show. This is the way to go.
AK: We went first thing in the morning. DId not feel the big crowds like at the other parks.
Weather-wise, it was cool in the early morning (shorts, t-shirt plus light jacket). By end of morning the jacket came off. It was warm enough to swim each day, but that could all be different this year.
All in all, I'd have to say I was prepared for alot worse crowd. It was crowded, don't get me wrong, but I've been there in August when it seemed just about as crowded. We were able to get character breakfast reservations, etc. Even walked up and did lunch at Cinderella Castle. Again, hit the parks first thing in the morning. People said that after the January 1 it gets slow, but it was quite crowded last year on Jan 2 & 3 as well. This year with Jan 1&2 being a weekend, I expect it will be vvery crowded until Jan 3.
More crowded, but the beautiful decorations and festive atmosphere make up for it.