First off, you have dinner which will take up around 90 minutes of the evening. This is always a high point for experienced cruisers - not solely for the food but for the rapport you establish with your dining room staff and the other guests at your table. I've lost count of the wonderful nights we've spent meeting others at our table. Important note here: requesting a large table is best. A table for 4 can be an invitation to hell if you are not compatible with the other two people. In that case, see the maitre'd ASAP and get changed to another table.
Beyond dinner, every night is filled with shows, bands, karaoke, comedy shows, etc. Not all of it every night, but a good mix.
You'll also be overnighting in Nassau so you'll find many passengers staying ashore that evening and visiting the casinos and nightlife there. Shops and ship's casinos are usually closed while in port, but I "think" Carnival has a deal to allow the ship's casino to open later at night if the ship is going to be there overnight.