Pros
Good chance to study Asian culture. Low taxes and social payments in Korea. Good benefits (including free healthcare and housing). Probably good for unexperienced engineers as a start, as the compensation and benefits are reasonable and often no special experience is required. Even though Samsung is very Asian company (see downsides), they are trying hard to acquire western corporate culture, so the situation will, probably, become better. If you endure Samsung, all other companies are piece-a-cake.
Kontras
Even though English is official company language, the ability of significant portion of employees to speak it is close to nothing. Do not expect your colleagues to share information with you, unless they have no other options. There is no chance for non-Korean to become a project leader (except for the case when you are hired as one). Head of your group may expect you to work overtime even if there is nothing to do, just to show your loyalty to the company. Difference in salary (at the same position) depending on the nationality. You may have a meeting to discuss problem of work and life balance. Starting at 8 pm. Really.