Family moved to NZ back in the 90s; I now live in Wellington.
1. Cost of living is higher than you might expect. Housing is ridiculously expensive in the main cities (not SF/NYC levels, maybe, but getting close). Food is also much more expensive than you might expect, especially some staples likes meat. Chicken, for example is almost twice as expensive. And as others have noted, the quality of the housing stock is awful. The typical kiwi house has horrible insulation, is very draughty, has no HVAC, and woefully insufficient storage, power points, etc. It's baffling.
2. Salaries are low, at least once you compare to the cost of living. If you're making the equivalent of USD$70k gross, you're doing pretty good; you then have to pay income tax which drops you down to around USD$52k net. It goes further than it would in SF, but given the cost of living, not that far.)
3. Country is lovely, people are nice, political system is very sane, the health care system works very, very well, the social safety net (welfare, unemployment) is not exactly generous, but it exists and works. If you can afford to live here, there are some enormous intangible benefits. And some of the benefits are quite tangible. Private health insurance exists but is hardly a necessity; even without it a doctors visit would be around USD$35, a prescription USD$4, a specialist will often be free due to government subsidies, emergency care is free at point of use, etc. Also, at least in Wellington, the public transit system is really quite good. Not cheap (...actually quite expensive!), but has a broad reach, very reliable, very safe and clean. I've seen MPs riding the bus to parliament; I imagine you don't see too many senators on the DC metro.
4. There are a LOT of startups around, a tech friendly culture, tons of meetups, lots of jobs, etc. There are big companies, small companies, SaaS companies, enterprisey outfits, machine learning startups, lots of argumented reality startips, accounting startups, etc., etc., and a lot of them are competing globally. Xero is probably the biggest success story, but it's the tip of the iceberg; there's a long tail. NZ is small, but the major cities don't feel like a backwater. Someone in another comment was comparing the cost of living to Tulsa, but you'd never mistake Tulsa for Wellington under any circumstances. :) It feels more like Seattle or Vancouver just...smaller.
I'm very happy to be here, but it's not for everyone. It's certainly different, there's a major culture change, it's not a clear-cut financial win, and the plane flight back to the states to visit family is hideously expensive and utterly unpleasant. But it has its pluses.