I just returned from Hawaii on NCL's Pride of Hawaii, March 26-April 2. I have two very strong suggestions. If you go with NCL, book your own airfare so that you will not be at the mercy of NCL's air. Their booking does not leave you enough time to really enjoy Honolulu. I suggest that if you do NCL's seven day itinerary, go to Honolulu two or three days early or plan to stay over after the cruise two or three days. The POH was a nice ship, but we were fortunate enough to have an upgrade to a Penthouse sweet which really made a wonderful week.
I personally am not a fan of freestyle cruising, but once you get the hang of it, it may work out for you. We enjoyed the speciality restaurants. If you book NCL, be sure to do your homework and plan your excursions before you go. Book a car at each port so you can truly see the islands. NCL's tour prices are ridiculously high. Also, NCL has limited activities on the ship and the entertainment if average.
If I go to Hawaii again, I am going to do the sail from some port to avoid the long flight. This way seems more romantic for an anniversary celebration.