I just took that cruise back on December 9th.
I was a bit surprised at how industrial the ports were, all but kona were shipping ports. Every port had a shuttle to Wal-Mart... We had excursions booked through the ship for most days, without excursions booked you'd be stuck doing a taxi or bus or something to get away from the dock. Cost wise, taxi's charged about the same as the "see a town" excursions scheduled by the ship, so you probably won't save any money if you plan on going solo without the ship scheduled excursions at any port. At a couple of ports I did see that some people pre-booked rental cars, the rental company picked them up and dropped them off at the pier. That's probably a good idea if you aren't booking an excursion. Except for kona, nothing worth seeing is near any port.
I did a dive in Kona, and the helicopter tour in Hilo. I don't remember the ordering now... (Just looked, hilo is before kona). The helicopter was never more than a couple hundred feet into the air at any time, it spent most of it's time quite low. At the lava flow we were probably less than 100 feet above it, you cold see the detail in the lava sloshing around. We then flew over to the coast to see the lava flowing into the ocean. It was cool because that night the ship did a night time pass by the coast to see the same lava flows. We also did the volcanos national park at hilo, it was neat, my son (4) loved walking in the cold lava flows and the lava tube. It was pretty chilly at the peak though.
We were thinking about doing the submarine at Waikiki, ends up there's no coral reefs in Waikiki, they're man made. So you're paying like $100 per person to see some sunken garbage and a few fish that have made it home. If you want to do it, do it at one of the other ports.
We have kids, so we didn't do the hailiahkala (sp?) sunrise bike ride. A friend that went with us did do it, and he said it was worth it. I saw the pictures and it looked amazing.
The molokini crater snorkel was pretty nice, right up near the sides of the crater there's some great coral a few feet under water. Can't get too close, it's a protected island, but you can get close enough.
The ship entertainment was OK... You don't do that cruise for the shipboard entertainment thogh.
Overall, I was mostly happy with the cruise, I just wish that the ports weren't industrial. I talked to someone about the other cruise line that did Hawaii cruises like this, I think it was Holland America (but not certain). It sounds like they stop off at better ports, but use tender boats more. The NCL itinerary does use tender boats at Kona, not other ports.
Hope that helps.
