We were on the Carnival Legend for New Year's two years ago. Frankly we were disappointed with the special activities for New Year's eve. They had a party on the pool deck but it was a crowded mess with a buffet, not any different than any other midnight activity that the cruise ships have - such as Island Night, Mexican Night, etc. I think we had a little "free" champagne, but again it didn't stand out as being special. They had TV sets in the bars, showing Jay Leno and the Tonight Show. That was essentially it! Nothing special happened on New Year's Day.
I have no plans to do a New Year's cruise with Carnival again unless the timing and mood happens to be right for me.