While I have read mixed reviews about the Oosterdam and this particular cruise in November in New Zealand and Australia, my wife and I can only say we enjoyed the trip.
We flew from Sydney (our home) to Auckland the day before and enjoyed the city ahead of embarking on the 14 nights cruise on the Oosterdam. HAL offered us a paid upgrade to a Neptune Suite which we took to experience the larger cabin and additonal on board facilities. It is a great way to travel if you can and we did not regret the extra cost. The Neptune lounge is a great facility and the Neptune staff were excellent and were always there to assist with dinner and excursion bookings, and went out of their way to assist us when bad weather caused a change of itinerary during the cruise causing cancellations of shore bookings. However the ports of call were great in New Zealand and the extra day and night In Melbourne a bonus to those of us who love the city.
While a number of pasengers complained about the change of itinerary due to bad weather, the Captain and crew made the correct call to alter the cross Tasman passage and reduce the discomfort due to heavy swells. On that issue the Oosterdam was impressive slicing through the swell with ease and was very smooth considering the 7 metre seas.
I love the Rotterdam deck, Quiet and great cabin in the middle of the ship with the Neptune Lounge across the corridor - very convenient.