Not having cruised with RCI I can't make any comparisons from first-hand knowledge. But two suggestions that come to mind: take advantage of the dining room for breakfast and lunch--the Horizon Court is really hectic at peak times; do see the big production shows, but try to get there 15-20 minutes early for good seats.
The Main Dining Room is definitely open on embarkation day until 1:30 pm or so. We boarded at 11:45 am this past cruise Emerald and ate there. Beware that they try to encourage people to go to the buffet when asked where the food is and do not mention the the main dining room unless specifically asked. Also, there is some great food in International Cafe on the 5th Floor = that was open too.