Things I love: the open spaces, the fresh food (compared to the UK, anyway; most produce is grown in NZ, whereas here it seems like everything is imported and stale), the people, Pacific culture, Lake Taupo, you can buy fresh falafel mixture at any supermarket.
Things I hate: public transport sucks, the cost of living is quite high, the current backward conservative government.
I've lived in Palmerston North (small provincial place where I grew up), Wellington (my favourite city in the entire universe) and Auckland (also a really nice city, but suffers from urban sprawl and can be hard to get around). Almost everywhere is expensive, but Auckland is off the charts expensive. I was studying and working part-time when I lived in Auckland, so it is doable, but it isn't particularly fun. If you want to try and figure out living expenses, take a look at listings on http://www.trademe.co.nz/flatmates-wanted
for flatmates (that's kiwi for room mates) for an idea on rent.
NZ hasn't traditionally been a particularly vegan-friendly place (it's built on meat & dairy exports) but the difference between when I moved to the UK in 2011 and when I visited in December was amazing. In part because of an awesome campaign called the V Sticker (http://speakupforanimals.org.nz/v-sticker-campaign/
) so if you do go, look out for bright green stickers on cafe/restaurant windows indicating that they serve vegan meals!
Happy to answer (or at least, try to answer) any other questions you have. Good luck!