I lived in Japan for nearly 2 years, way back in the early 90s. I became very critical of the culture, which I think is closed and opaque - it is in hospitable for learning a language, as many Japanese turn off when their language comes out of a foreigner's mouth. You can never get integrated into the culture.
I do not know Korea. But the one thing to keep in mind is that Korea is viewed as on the way up, while Japan has been stagnant for 20 years.