We were also on the inaugural Honolulu to Sydney sailing!
Agree with the points made by previous posters, but adding that the photo scavenger hunt was fun for adults, too-- we have done them on other long sailings, and it's a good way to get your steps in, and explore the ship, looking at the details.
OP, if you like sea days, this is a great cruise! We love the sea days and between relaxing, visiting with characters, the regular on board activities (bingo, trivia), we made a point to go to the lectures by the guest lecturer, who on our sailing was a photographer from
National Geographic. Not only were his talks interesting, but he also taught us some things about photography. We did not go to the Anyone Can Cook series... the guest chef on board had a huge following, and people would line up for an hour prior to the cooking demos.
Agree with PP about dining-- by the end of the cruise, we would eat on deck, or just order an appetizer, or main, or skip dessert-- something to not eat huge volumes of food every night. But the menus were overall very good-- they bring out different menus on the longer cruises, in addition to the usual menus, so you are not totally repeating options.
Ports-- we did an independent tour in American Samoa to visit the National Park, which I thought was a good tour. It basically took up the entire port time. The people of American Samoa were so friendly and welcoming! We did a ship excursion in Fiji to the ColoSuva Forest/Park, which was good, but one could always book that transportation to the park independently. Since we were in Fiji on a Sunday, the main markets were closed-- but I hear they are very interesting. Also, we originally were supposed to dock in Noumea, Fiji, which I hear is more scenic, but a few months after booking the cruise on opening day, our port was changed to Suva. I believe that limited the offered excursions.
We did an independent excursion in New Caledonia to snorkel with sea turtles.
There were not a lot of kids on this cruise (300-400) and it wasn't full (about 1900 passengers? I don't have my notes with me). So it never felt especially crowded.
Crew talent show is a must. They had special events for crossing the equator. Crossing the International Date Line wasn't a big deal, other than losing a day. The ship building contest they do on these long cruises was fun.
Seas were generally smooth until the last 2 days, as there was a tropical storm to the north of us, and a cold front coming from the south, so the last sea day was bumpy.

(we like that)
We enjoyed Sydney. Note-- factor in the cost of a one way ticket from Sydney to wherever you live. That was almost as much as the cruise cost itself! Also, if you plan on staying at Aulani prior to the cruise, be ready to book at 11 months.
if you have any questions, don't hesitate to ask!