We stayed at the Suissotel in Sydney (arranged by Holland America, whose representatives met us at the airport, took us to the hotel, and transferred our luggage onto the Volendam the next day). Beautiful location, making the city easy to walk around and enjoy.
Check-in on Volendam was seamless. Melbourne was good for walking, Burnie for the animal preserve visit.
Luckily, the Tasman Sea was calm when we crossed! During this crossing, you will need to be prepared for a long wait in a line (1.5 hours) on the ship so that New Zealand customs can check your paperwork and your shoes (make sure you wear a clean pair). Enjoy this time by chatting with those around you or reading a book.
The option of leaving the ship at Milford Sound and crossing on land (overnight) to Dunedin is well worth the cost. Visiting Christchurch when we docked at Akaroa (site of 2 earthquakes in 18 months) was very moving experience. Picton (nature tour), Wellington (walked to museum), Napier (wineries) were great ports. The excursion to a Maori village in Tauranga was OK, not spectacular, but the hike up Mount Maunganui made this port very special (you can walk to this location from the ship).
Auckland excursion to see sheep herding and shearing was a perfect way to end the cruise, and our luggage was waiting for us when we were driven to the airport.