I did this itinerary a couple of years ago and loved it. We used private taxis in most ports (Auckland and Sidney are the exceptions) and found that this is the way to go. We took a ship's shore excursion to Rotorua Lake for trout fishing and were sorely disappointed and found that a simple taxi driver would have put us on much better fishing.
Here is a link to the review with blow by blow descriptions of each port.
Have a great cruise!