We love this time of year at WDW - busy, but manageable, especially if you are veterans, who know how to utilize FP, use early hours, and hop as needed. If you haven't been when it is decorated for Christmas, you will love it! Seeing the castle lighting is amazing and the giant gingerbread house at GF is a must-see. Love the feeling on Main Street and the corny Christmas jokes on the Jingle Cruise! We also enjoyed the Candlelight Processional at Epcot for conveying the spirit of Christmas. You will want to reserve some time to resort hop and see all the decor, or plan to eat at some of them to check it out. WL is especially beautiful, with a similar look at AKL. Monorail resorts as well as Epcot resorts have displays.
If you are well planned you can work around the crowds - it is definitely better than Christmas week! Weather can be very warm or cold, we were in shorts one year on Tday, and wearing winter coats and gloves on another. We actually found the day after Tday at MK the busiest, so I'd avoid that. We went early to MK on Tday, had lunch at LTT on year, and dinner at 1900PF another, in case we wanted to leave if it was too crowded, but didn't have a problem - sorry, just realized you will hopefully already have your days planned since it is only a month away(wow!), but hopefully still some helpful info!