I really loved Queenstown, there were loads of trips to do, and exciting (and dangerous) activities. We flew to Milford Sound, which I loved but my husband hated because it was a little 6 seater plane. You can also take a coach, and the most popular thing is to take a coach one way (about 4 hours) and fly the other way (about 45 mins) so that you get to see the scenery. I also really loved the glaciers, we stayed at Fox glacier, we took a helicoptor trip that went 'round Mt Cook and landed at the top of the glacier so we could get out and walk around. Also the drive between Queenstown and the glaciers was astonishingly beautiful, and there was hardly any traffic.
Rotorua was interesting, but 2 nights would be enough time there. I thought the museum was particularly good, and it's worth splashing out on a motel with a spa bath in the room. We stayed in Christchurch but found it a bit boring. Auckland was quite nice, but it was only interesting because they were doing the America's Cup at the time.
If I were going again I would try to visit Te Anau (way down south) and the Bay of Islands (in the north), and the Marlborough Sounds area.
We stayed in some really nice, comfortable places and in some so-so places (not bad, just not special) but they were all very affordable. I can't remember all the places, but I can look them up if you like.