We've very recently updated our New Zealand guide with input from expats on the ground. I'd recommend you have a look at it, as it gives a good overview of what you can expect. The guide starts with Moving to New Zealand.
I'd especially pay attention to Culture Shock in New Zealand and read a few of our interviews with expats in Expat Experiences in New Zealand.
It is difficult to strike a balance between online naysayers and the glossy reviews of travel guides. It is also unfortunately a case of seeing whether the pros outweigh the cons, which is a very personal thing.
Hope this helps,