I lived in Christchurch for a year prior to moving back to California. The rock climbing in NZ is not nearly as good as what we have here, but if you know where to look, it can be pretty fun. Pick up a copy of this book for the best overall coverage of where to go:
Castle Hill is world class bouldering, mostly on slopers, just outside of Christchurch. It was not much further than an hour, close enough that we went after class a couple of times a week. The crags in the Port Hills around Christchurch are also good, they're where I learned to trad climb.
Didn't make it down to the Darrans for climbing, it was always wet when I went down there. The granite looked great if not covered in moss, etc. due to the incessant precipitation that falls in this area.
There is a cool multi-pitch sport crag just south of Mt. Cook Village, the views north to the Mt. Cook Massif are incredible.
Check out Payne's Ford in the north of the South Island too for sport climbing on steep overhanging routes.
I'd say the best climbing in NZ was the alpine ice, but if that's not what you're looking for I'd check out that book and see what you can see. Feel free to message me if you've got any more questions.