We've been on several RCI cruises with many sea days (multiple Transatlantics, and a 34-night cruise around Cape Horn).
RCI does a great job of activities on sea days. The Enhancement Lectures are a favorite of mine. My DW enjoys those as well as the crafts classes. There so many other activities: trivia, bridge lectures, mixology, fitness classes, dance lessons, movies, and more. The trouble is deciding when activities overlap.
One of my favorite lecturers on RCI is David Kirkpatrick, former Studio President of both Paramount Pictures and Disney. He was involved in the production of over 250 films, including: see
video montage.
Don't miss him if he's onboard. He has incredible stories to share -- including when, as a child, he heard Walt Disney was ill, wrote him a get well letter and enclosed an 8mm film he and his brother made to lift his spirits, and how Walt's reply led to a career in movie production.
Woody