Just got back from a New Zealand cruise on Sun Princess. I highly recommend this ship. Big but not too big, and the crew - mostly Phillipino - were excellent.
A couple of tips: Avoid the feeding frenzy at the buffet and use your allocated sitting in the dining rooms for breakfast and dinner. Purchase a "coffee card" $35 for 15 specialty coffees. If you are into non-alcoholic drinks including "mocktails" purchase a soft drink package - excellent value according to fellow travellers.
Interesting thing about this cruise was that there were very few children (less than 10 according to the crew).
Sun Princess is now doing an Aust east coast cruise on its way to Japan for a while.