First trip on NCL, and our family of 7 (teen to seniors) had a great time. Ship was clean, steward was excellent, drinks very good. I was afraid I had made a mistake booking this ship after seeing a number of poor reviews for Oct-Nov of 2015, mostly on the long boarding/disembarking process and over-run bars with very long waits. But perhaps NCL read them too -- no long drink waits, and we had an easy time getting off, by carrying our own luggage off.
DINING: Only difficulty was inability to make reservations at some of the specialty dining rooms (2 in the party chose the free dining package over the free drink package). You need to reserve those early - before your trip, or early in the week. The French and Brazilian-style specialty restaurants (read - extra $ if you don't have the package) were great -- fabulous food. But we were unable to take advantage of other restaurants, in part due to wanting to eat all together, and in part because we couldn't get reservations.
EXCURSIONS: As others have indicated, booking with a local tour rather than through the ship has the advantage of saving 30-50% (however, you may have to wait to get off the ship/get on tenders until NCL tour participants have disembarked -- this was a problem only in Belize, when sea was rough and we had to wait a couple hours to get a tender). I checked toursbylocals.com and viator.com as well as cruise critic and travel advisor. Friends had recommended excursions in Roatan and Belize (you don't want to be walking around Belize City!) Had WONDERFUL family experiences snorkeling in Roatan (with Roatan Ocean Adventures) and cave tubing in Belize (with Cavetubing.bz). Both were excellent. Took taxis/rented golf carts in Costa Maya, and in Cozumel, took a taxi to the Money Bar and went snorkeling off the shore (had drinks and some food, with table/chairs on the beach as well as outdoor shower, with no extra charge).
GYM: Some of our group made use of the gym equipment daily. No major crowds, good equipment, had supervisor to answer questions/help.
Overall - a great family time over the holidays!