Hi!
Christmas at DLP is fantastic - the main park in particular is beautifully decorated. There are Christmas shows, the Christmas parade, the Enchanted Fairytale Ceremony (tree-lighting), Fantillusion (night-time parade), Christmas market, Belle's Christmas village, plus you can meet Santa and lots of the other characters in Christmas dress. There are lots of nice touches like carollers on Main Street and "snow" falling.
If you go during term time, the park will not be too crowded as long as you go during the week. The weekends are entirely different though - be warned!!! We went 11th December last year, which was a Saturday - the park was absolutely packed at the weekend - over an hour for all rides, Fastpasses gone by lunch and we couldn't find ANYWHERE to eat till 3.30pm!! Yet for the rest of the week, it was absolutely fine - we were able to walk onto most rides without much of a wait at all. So if you can avoid the weekends and any time when the kids are on holiday you will be fine.
We've been 3 times now, and each time we go for 4 nights. For a first time visit, especially for Christmas, I think you would need this long to do everything. Although of course it depends on how many of the rides you want to do, how many of the shows you want to see and how much shopping you want to do!
There is one negative point - the weather! It was absolutely FREEZING!
Really unbearably cold - we were wearing as many layers as we possibly could and were still really cold. In fact it was so cold that I don't think we'd go in December again - this year we're going on November 6th - the Christmas festivities start on 5th November so we'll still get to go to the park in the Christmas season, and for the Bonfire celebrations, and hopefully it'll be a bit warmer!
Anyway hope that gives you some idea, of course it's just my opinion but if you have any other questions please ask!
Rhiannon