Rotational dining means you don't eat in the same place every night, and your schedule is predetermined before you board the ship. There are usually two time slots you can choose from — we were given the options of 5:45 and 8:15. Depending on what cruise you take and on the length of your cruise, you and your party will rotate through different themed restaurants, staying with your same servers throughout your trip. This allows you to build an awesome relationship with your servers; by the end of my cruise they were able to suggest items on the menu based on my personal tastes, and I didn't even have to ask for my drink when I sat down each night.
On the seven-day Disney Fantasy cruise, each restaurant on board had a night featuring a special menu, like "Prince and Princess" night, and very special menus for Star Wars Day at Sea. Animator's Palate restaurant put on two great interactive shows on the screens in the dining room as well.