I made the move in 2006. Lived in New Zealand for the next ten years (returned to the U.S. last year). I'll try to give a detailed, informed picture instead of a quick summary because...well, I'm bored at work right now and it's friday, so why not.
Initially, I loved it. I was young and open-minded and it is easy to romanticize that kind of relocation for a while.
I found work and got comfortable enough there. After a year or two or three, the scenic country-side and beaches don't matter as much as you're just bogged down in the routine of living life.
Culturally, Auckland is an interesting place. I believe over 50% of the population there is non-white/european. Lots of asian immigrants come there as well as peoples of the middle-east, India, the south pacific and elsewhere. This means a thriving international community with plenty of good restaurants and food courts. Most of my friends there were not native kiwi's. As a matter of fact, I found it hard to make friends and break-in to the native kiwi social groups. My theory there is it was just easier to meet and mingle with internationals who didn't already have a social clique.
Most Kiwi's are fairly liberal (at least in Auckland), and most do travel overseas at some point and have a larger world perception than average I'd say. Though I found some attitudes and local social norms to be a bit dated. Kiwi's in general are non-confrontational and as an American you can often find yourself being over-bearing or over-stated simply because people don't share their opinions as vocally. They love Rugby and Cricket as much as Americans love football and baseball. Drinking is a large component of the culture and workplace. Most work places have Friday drinks and you will find yourself alienated if you don't participate. The youth start drinking way too early as well.
Weather-wise, it is chilly most of the year, but not severely cold. Auckland has a rainy/drizzle season that overlaps most of the winter. Hardly anyone has A/C and those that do, don't use it because electricity is not very cheap. Luckily the Summer doesn't get too severe and doesn't last too long.
Work and career-wise, Auckland has most of the job opportunities. I felt people were generally underpaid and there was not a lot of disposable income but I suppose it all depends on your career. Most work places are outdated in their attitudes and are practicing what was popular easily 10-15 years ago in the U.S. But again, this largely depends on what you do and how big the company is. Holiday benefits are great. A full-time employee gets 4 weeks of paid holiday per year, plus two weeks paid sick-leave, plus all the public holidays (almost another 2 weeks worth). As a permanent employee, it's also harder to get fired. People generally didn't fire employees unless they do something illegal or keep repeating some grave error. They usually are forced to get rid of you through re-structuring and lay-offs (redundancies). Unions have fallen out of favor though they are still around and relevant in some cases. A lot of companies unfortunately are using loopholes, like hiring you as a contractor or giving you less than full-time work as to avoid paying full holiday benefits. I often worked as a contractor until after 5 years in one place I was able to finally get in as a permanent. Taxes are not nearly as bad as you might expect, especially with the near free healthcare. Sales tax (GST) on the other hand are at a ridiculous 15%.
Healthcare, there are pros and cons. Generally my experience was good. All hospital visits are free. Any accident of any nature is generally covered by what they call ACC, which all residents have. Think of it as an accidental injury insurance that's mandatory. If you register with a local doctor, you'll pay a subsidized rate for your visit, something like $25-60, depending on the place. Babies and Children go for free. Subscriptions are also heavily subsidized and I think you'll pay like $10 per prescription fill though I can't remember exactly. Some people do purchase private health insurance though most don't. We ended doing so for our kids because it wasn't much and it helped in a few scenarios. Adults do not get any Dental healthcare for free and dental insurance is expensive or hard to come by. This is by far one of the worst expenses you'll face regarding health costs. Kids do get free dental care till they are 18 though. The hospital and healthcare system has a tendency to work in slow-motion. Hospitals are understaffed and over-worked and people sometimes wait months to get an operation scheduled if it's not urgent. This is where the private health insurance can speed things up.
Love-life/dating/marriage - If you are not already married, your prospects are good here. Auckland has over a million people in the area and chances are you will find someone if you look hard enough. Do not count on meeting people organically. findsomeone.co.nz is the match.com of New Zealand. You're probably better off meeting someone there than you are at a club or pub. I went on dozens of dates using online dating services and no one ever thought it was weird that I talked to. I found my wife this way, a university student, studying in Auckland and originally from China. We have two kids now and are happily married. If you are looking for that commitment, and enjoy going out, there are plenty of "meat-grinder" clubs that people go to specifically to hook up and Auckland has a vibrant nightlife scene (which quickly tires for anyone past college age years). There are even some cool places that don't focus on hook-ups, like jazz-bars, etc.. And if you are looking for even less commitment, you're really in the right place because prostitution is legal in NZ and there are plenty of message parlours to choose from with many exotic, international girls. Legal or not (I suspect some of them don't have the proper licenses in any case), these places are as shady as you'd expect. I'd probably advise staying away though I had a few friends that indulged and loved these places and I'm not judging...
Cost of living and housing, in Auckland these are not cheap. 3 bedroom bungalows 15 miles outside of the city could easily cost you $500,000-600,000 USD or more. A lot of products are imported and more expensive due to New Zealand's geological isolation. Food and eating out have inflated to prices I could not justify easily. Still there are deals to be had. Find a $5 kebab in the city or a $5 pizzahut deal and you're good to go, right? I made my lunch most days and even went on a tuna sandwhich binge after we bought our house. Product variety and competition are significantly less than the U.S. and as a result, most things cost more. We did not have any expendable income. Almost all of my wage went to paying the mortgage and my wife had to pay for the utilities, and food costs out of her salary, usually leaving nothing. Luckily, we were able to snag some gov't subsidized help on the children's daycare. When I lost my job through re-structuring, I spent about 9 month unemployed, and if it wasn't for my Wife's mother, we probably would have had a house. There is a safety net in NZ and if you are poor enough (basically without any income), you will get enough from the gov't to house and feed you and your kids. It won't be pleasant but you wouldn't end up on the street.
Retrospect or hindsight or whatever you call is a strange thing. I guess I'll always love NZ in some ways. It was my home for a decade. I met my wife there. I had friends there. I probably regarded it as better than the U.S. for most of my time there.
In recently coming back to the U.S. though, I have come to recognize how truly different we are (some might say lucky). Without a doubt we have the most comfortable life-style, the most modern conveniences, the most overall accessible, luxury lifestyle that you can get. We also make more money at our jobs, though we work harder. We have thousands of choices in our consumer lifestyle, cutting technology in products and services that the rest of the world is denied, and we get it all for dirt cheap. Am I saying that all of this is good or healthy? I'm not going to get into that but I have decided to move my family here because, a) I want to make them comfortable and to be able to afford basic needs for them more easily (like being able to heat the house during winter so you don't wake up to find they discarded their clothes and blanket in the night and are shivering cold). I won't get as much time off but at least I can freaking afford to take them to disney world when I do, which is better than 4 weeks off, spent at home because you have no money. I want to feel confident that I can make a living and get a job and I want my children to have those job opportunities when they get older as well. I also want them to have the ambition and confidence to follow their crazy dreams (something I saw disturbingly lacking in the culture of New Zealand). I don't know what it is about us americans, maybe we are too stupid or have our heads in the clouds, or maybe there are just more opportunities, but we have a tendency to just go for it in a way I didn't see often in NZ culture.
In conclusion, I'd say that for me at least, NZ was probably a great place as a single and even the early years of my marriage but with having a family, I'll take the mod-cons and financial elevation of the U.S. over the thread-bare existence we had in NZ. Maybe it's all a system that is doomed and going to collapse or whatever but like how surfers go to where the waves are, the waves are here right now and choosing whether I want my kids to be New Zealand or American, I still think they'll be better off being American.