We were there last year Dec. 19 - Dec. 28 ---- Crowds were bad, but tolerable up to Christmas. On Christmas, they were turning away cars from the parking lot at 10:30 am - and they closed the park around 11 to new visitors. Ridiculously crowded. Now - IF you go to WDW all of the time (we are on trip #34) and only want to take in the atmosphere and parades, etc. then GO --- but if you want to go on all of the rides all day long - then be prepared for 3 hour waits for the bigger rides (or longer).
We would hit the parks at opening, ride a few rides - then be back at our resort by 11 am for relaxing - then off to dinner and fireworks. That worked great with minimal crowds - but most people show up around 10 - 11 am and stay until closing (midnight)......Jill