When I started playing this one, after a couple minutes I realized I had no clue what was going on. A case of bad timing--I was on my way back home from my first SF convention ever, where I'd given my first novel pitch to an editor, which I thought went well, and my mind was spending much of its think-cycles thinking about the pitch and figuring out what parts of the story needed to be changed.
So, I wisely decided that I should start from the beginning when I wasn't so distracted, and I really enjoyed it! Once I was devoting sufficient attention to it, I picked up the slang very quickly. I was already pretty familiar with Kiwi accents (thanks Flight of the Conchords), so I didn't have too much difficulty with that, and I think her voice went very well with the story. The slang was all very intuitive. I'd guessed "arties" meant "artists" before I listened to the story so it probably helped that I didn't have the word "artificial" stuck in there. It introduced Tinmen quickly, which I pictured as Tin Woodsmen and probably police (tin badges in the wild west), then shortly thereafter referred to them as pigbots which reinforced the robo-police perception which turned out to be true. It took me a few iterations to realize what Thicknecks meant but it followed from the other classes without much difficulty, no biggy.
I did wonder what put the world in this state but it made more sense NOT to tell us, because the narrator would not have known. Apparently some kind of biological blight has occurred to make non-human life nonexistent or scarce, and whether in parallel or separately, people have made designer children. Although each has an enhanced specialty I didn't see it as being that they had any actual reduced potential in other areas, it's just that in those other areas their potential is unrealized. Their parents chose a specialty for them and they expect their kid to fulfill that specialty, even though it means taking time away from being more well-rounded. The idea of having to be forced into just one specialty area is sad to me--I am neither right nor left-brained, but taking each in turn. I need both in my life to feel satisfied. So I work in engineering to satisfy my logical side and write fiction to satisfy my creative side. I liked that the most important figure in the story is the one who is able to grow past his expected boundaries.
I thought it was interesting that the Brainiacs couldn't create, but seemed happy to just study what already exists. This makes Brainiacs and Arties a perfect pairing because the Arties create but don't understand, and the Brainiacs understand but don't create.
As far as the question of why the arties are suppressed and out on their own, I assumed that rebellion was a part of their artistic nature. I figured that they were created to stay at home and serve a function to their parents making things beautiful. But the arties rebelled, thinking that fulfilling a purpose instead of creating art for art was like selling out. So they go out and find a way to express themselves that is NOT approved/sanctioned by graffiti and the like.