I went to South Island a few years ago. I spent a couple of weeks making my way from Christchurch via Queenstown to Te Anau (sp?) and Millford Haven.
I have to say that the scenery is spectacular. We passed a lake (Tekapo?) on our way to Mount Cook. Because of minerals dissolved in the water, the lake is naturally a vivid turquoise colour - like a swimming pool, or something dreamed up by a fantasy artist. Truly amazing.
At Te Anau, we went on a boat ride through some caves where there are thousands of glow worms. That was very interesting too.
The temperate rainforest around Millfor was impressive. Unfortunately, the weather wasn't too good (it usually isn't around there), which was a shame. I think that the southern fjords on a sunny day could rival the Norwegian ones.
The only drawback to whole trip was how we were treated by the NZers in most of the tourist spots. Essentially, if you weren't Japanese/didn't spend lots of money, you were persona non grata. On one particularly long coach trip, the whites were made to sit at the back of the bus (I'm not kidding).

The NZ tour guide gave explanations in Japanese, but not in English. And when we stopped along the way, the whites were held back so that the Japanese could go to the shops/restrooms first.

When my mother complained, the NZ tourguide laughed in her face!

We also thought it was strange that the official signs in the park in Christchurch were in English and Japanese, and no other language.
BTW, I'm not anti-Japanese. My GF is Japanese. I just don't like being treated that way.