christchurch is a bit of a dump and very bland although it is in the south island. Wellington is the place to be. Small city with a bigish city feel and excellent riding-I'm bias though, I live here.
Holidays-legal minimum is 4 weeks annual leave and 11 days of public holidays and not sure what someone was going on about US voucher system.
Crime rates are low and you don't have the muggings, etc that happen in big cities in the UK. There is crime but it isn't something that has really ever affected me apart from the house being broken into once. That said I leave my 5-spot parked up outside my front door at night and it is still there in the mornings.
Certainly I would give living in NZ a go. Job wise you'll find you'll need to be more of a generalist and be able to cover a range of tasks and companies here are not so hung up on specific skills but generic transferable skills are highly thought of.
Place isn't perfect, but no place is. I would say quality of life is much better than the UK by long shot. Food is local, people are friendly and approachable.