I'm doing my PhD at a tier-1 Korean university. I am one amongst a quickly growing cohort of international grad students, and am very satisfied with the level of instruction and support we receive. Lots of funding through the department and BK21, many opportunities for research, presenting at confs here in Seoul and publishing. Also, the research environment in Korea is very dynamic, so there are a lot of opportunities here for someone willing to work hard and do their best.
My two Won.
Unless you are doing something Korea-specific, please note that publications in proceedings of domestic conferences and in domestic journals are of little value outside Korea, especially if you have academic ambitions abroad (after obtaining your Ph.D.). The same holds currently true for publications in Japanese and Chinese journals, although some of them are indexed by SCI/E. You really need to aim at refereed publications in international conference proceedings and journals that are well-known in your research community.
In addition, Korean domestic journals do not have a strong reputation…:
http://www.nature.com/news/2008/081008/full/455715a.htmlAlso, an important difference exists between working hard and working smart, a distinction often not made and not appreciated in the Korean workplace and in Korean labs... A Ph.D. student typically needs to work both hard and smart.