I've spent lots of time in Seoul, at one point crashing in the walk-in closet of a friend for a few weeks. The apartment was pretty small by American standards, the hallway between the front door and the bathroom was a little wide, with the extra space taken up by a counter, fridge, sink and two burners as the kitchen. On the other wall of the hall was the door into the closet. Down the hall next to the closet was a very sparse bathroom that was effectively a powder room (toilet + sink) with a shower hose on the wall. And at the end of the hall was a small bedroom that fit a queen size bed and a small desk and not much else.
In the U.S. I live in a fairly large house and was pretty concerned about the small living area. But it worked! Everything is kind of geared to support that kind of living arrangement. If you sleep on the floor, by rolling up your bedding in the morning you suddenly have a living room. Fold out tables and eating while sitting on the floor and you have a dining room that can fit (not a typo) 8 people reasonably comfortably. The floor of the closet had room for me and my wife. And since the floors are heated in Korea, even in the winter we were incredibly warm.
To eat you buy what you need for that day, or even that meal at the grocery next door, and your frequent trips in and out of the apartment give you plenty of time to bring out trash and other things.
Feel cooped up or want to do some kind of activity like play video games or drink and chat with your friends (but don't want to disturb the neighbors)? There's literally an entire city full of services designed for the apartment dweller, everything from cheap Internet Cafes (something like a dollar an hour), to cheap bars with private rooms for your friends at no extra cost!
Other than sleeping and a few meals, we really didn't spend much time there, instead spending almost all of our time out and about. It really is just an entirely different way of living - not better or worse, just different.