I was on this cruise. It was a blast. I was not overwhelmed by the crowds. Like another poster said, you can chose to not follow the crowds and still have a great time. We stayed on board in Nassau and enjoyed the ship. We dined at Remy for brunch and dinner (no crowds there). We spent time sitting on the veranda listening to my cruise music play list, Aquaduck, bars, shows (golden mickeys, believe, wreck it ralph), Mixology, snorkeling on castaway...The list goes on. I am surprised at how much we were able to do in five days.
As for the "holiday" part of the cruise.....Disney sure made it special. To all the little gifts left in the room (as mentioned above), to the santa/reindeer ice sculpture, all of the holiday decorations, the man sized gingerbread house, the gingerbread decorating event, special main dining room meal, etc....I walked around in amazement half the time. I was really impressed on all of the character interaction my kids got. It seemed like every time we turned around....Mickey, Minnie, Goofy, a princess (Ariel actually walked my 2 year old down the hallway), Donald, Daisy, all of the characters all decked out in their Christmas outfits. Never a long wait (rarely more than a minute or two) for the kids to interact with them. It was great. Not sure if this is the norm or if they had extra appearances because it was Christmas. The extra 200 in OBC presented on Christmas morning in our stateroom was also a nice touch (ok, I am kidding about that one).
All in all, I would highly recommend a holiday cruise.