My family and I cruised on Christmas Day in 2017 on the Dream and would do it again.
Christmas Day fell on a sea day so it was very relaxing.
Disney offered a Christmas Eve service and a Christmas Day service in one of the theaters.
On Christmas Morning, the atrium had Mr. and Mrs. Claus and snow was falling.
DCL provided an assortment of cookies and beverages (hot cocoa, apple cider, and such) to nosh on. Children under 18 were given a DCL Tervis style mug. All cabins received a piece of DCL Christmas theme wall art.
I enjoyed seeing families in matching pajamas\robes strolling in the atrium. Some of the matching pjs\robes had embroidery, stating the family position. Example is Grandpa, Grandma, Father, Mother, Daughter 1, Daughter 2, etc, etc.
Here is the Christmas Day menu from the Wonder in 2016 and it was the same for us on the Dream in 2017.
Hope this helps.