My three girls and I were at the BC from Dec 25-Jan. 3 this past Christmas. The crowds are large, but if you get up early and take a break in the afternoon before heading back to the parks at night, you can get plenty done. The worst for us was having to get to the MK by 7 AM because they were early entry every morning that week! We loved being at WDW and keeping the feeling of Christmas going after the day itself -- everything was so well decorated and there were still the Epcot Holiday storytellers, Candlelight Processional, Christmas parade at MK, MGM, and Ak, etc., when we first got there. We love spending New Year's eve at Epcot, too. Even though the crowds are large, the space there is large enough to handle everyone.
I don't know if it would be a good time to select for your first time at WDW, but we have been many times and really enjoyed our trip between Christmas and New Year's.