I lived in South Korea for 3 years and 4 months. It would be a cliche to say that they were the best of times and the worst of times. Frankly, they were all pretty good, even when I was having my appendix removed.
I learned a lot while I was there, although mostly I think I learned about myself. Living outside of your culture leads to many discoveries about your comfort levels, boundaries and assumptions. You also change a lot of perceptions. When I returned to Canada, there were many things that hit me as strange.
The air was noticeably cleaner. Koreans say that their air pollution problems arise from China, but I think that some day they'll have to take responsibility for it themselves, then the country will get better. Ditto with the water quality. It can't all be someone else's fault.
For what it's worth, the Koreans have a very good public transportation system, and it is widely used. But, they also really deter pedestrians with a bizarre system of traffic lights that endangers anyone brave enough to not be in a vehicle.
The buildings in Canada are so short! The tallest building in South Korea is only 63 storeys tall, but so many of the buildings are so tall that you never get long sightlines or distant horizons (except when you live on the coast, which I did for the last year). It's true that the CN tower in Toronto is much taller, but the average building in South Korea has got to be 10 storeys.
The biggest impact that I felt when I returned was how much my definition of personal space had changed. I would go to the mall to Christmas shop, and my family found the place to be very crowded (finding a parking spot was very hard) but to me the place was empty. Where were all the people? At no point in my Christmas shopping did I find a store as crowded as E-Mart was every weekend.
It's an odd thing about being a teacher that you become attached to a group of kids, then they're gone. I'll never see most (if any) of my students again. What will happen to them? Will they be happy? I'll never know. It's a saddening thought. I'll give one group of them the final "word" on Korea:

— SGP