I spent 5 great weeks exploring New Zealand, I saw most of both islands and with a couple more weeks I could have covered what I had to skip. My travel advice is that if and when you go to NZ, give your self at least 1 month per island and more on the South Island if you can. I would recommend flying into Auckland and renting or buying a camper van, then hit the road and fly out of Christchurch on the South Island. Something like that....
lots of dolphins in the Milford Sound
always nice to see a rainbow!