i've been at xmas. One thing to remember is that it does get pretty cold so make sure you got some warm clothes and a coat for the evenings.
Everything stays open right through so you needn't worry about being stuck in your hotel room with nothing to do on xmas day/night. We were worried prior to going that we'd have nowhere to eat on xmas but theres so much choice you'll have no problem. We ate @ the Monte Carlo in the buffet restaurant, although there is also plenty of A La Carte dining also. It came to $15 each and believe me there was no scrimping on quality regardless of the cost. We were stunned!
There will be gala events and shows or trips but you'll probably need to book these in advance.
The decorations inside the hotels were wonderful when we went (4 years ago) so there was plenty to look at, as you know they really go to town and xmas is certainly no exception.
You'll have a great time, i wish i was going!!