My husband and I sailed with Norwegian for our honeymoon, and had a wonderful time. We had a mini suite which I highly recommend because you get concierge service, and we took advantage of this more than once (dinner reservations, shore excursions, etc..). Plus the balcony was wonderful to eat breakfast on!
We enjoyed the food onboard and tried most of the speciality restaurants. We really liked Endless Summer. We liked being able to eat whenever we wanted, and to have the option to eat alone. Also, they will save your wine for another night if you don't finish it.
I recommend booking all of your shore excursions before you cruise (which we did), because the line for them looked long. We also really liked our trip to Fanning Island. It was a once in a lifetime experience. We booked the excursion to the private beach, and it's well worth the extra money. It was the most beautiful beach we have ever seen, but make sure you head to the other side of the island for the BBQ.