I studied at the University of Auckland for their second semester, and overall I think I just learned how to live on my own a lot better.
As I wasn't part of a study abroad program, when I came to Auckland I was immediately left to my own devices, and it was up to me to sort everything out. My first grocery shopping trip resulted in me buying a lot of expensive canned and pre-packaged goods, but now I'm buying enough fruits and vegetables to go with my Tim Tams and to make my mom think I'm at least trying to be healthy.
While I think UoA definitely leaves everything more "up to you" when figuring things out, I think the independence has helped me grow a lot as a person. I've gotten a much better hand on my time management, organization skills, and cooking skills since I've arrived... as well as being more capable of navigating new social/administrative situations on my own.
As for exploring the rest of New Zealand, I ended up doing a hop-on hop-off bus tour of the South Island during the mid-semester break -- easily one of the best, most unforgettable experiences I've ever had.
What would you improve about this program?
The one major downside was probably just being so confined to Auckland, as a student without a car. The benefits of being so close to the city centre mean that grocery stores, banks, bars, and Giapo were almost all about a 5 minute walk from me, but there isn't much to do tourism-wise around Auckland without giving up lots of money. I wanted to get out to do more touristy things, I'd either have to get a car and drive around New Zealand by myself for book some expensive trips. The public transport doesn't get you to most tourist destinations even around the North Island, so a car is the most ideal way to explore. Also, because I wasn't part of a program, it wasn't as easy for me to arrange trips with people to go out and explore the rest of New Zealand.
As for UoA in general, a little more guidance for more administrative things would be helpful (finding housing, getting classes, etc) -- other than being told where to pick up my ID, I wasn't told much else. I had to figure out housing, grocery stores, and the rest of that mostly on my own. Classes, although relatively easy in workload, were quite similar in their lack of guidance and expectation.
A few more social aspects that I struggled to deal with personally were just making new friends and going out, since I wasn't part of a study abroad program. Since the school is so big and lectures are mostly just to listen to the professor, if you don't make friends in tutorials or with flatmates (who are mostly in already formed social groups), you're a bit out of luck. I wanted to meet more locals, but since their groups were mostly established, it usually ended up being easier to befriend fellow study abroad students. While I enjoyed going out, I started at some point to feel like I was socially obligated to go out and spend money to have a good time -- something I wasn't really keen about, especially since drinks/food are usually about $8 and $14 respectively, on the conservative end.
My advice overall would just be to have a plan for when you go abroad! Figure out what you want when you're going abroad. I came to NZ without really knowing what I wanted other than a biology class and to explore the country, with no plans set for the most part. Thankfully, I met other study abroad people who knew where they wanted to go/what they wanted to do and they helped me out, but otherwise I would've just been stuck in Auckland for 4 months.