Pros
Free food and good medical insurance plan as other mentioned. Opportunity to work among many young fresh graduates (as they can only attractive no-experience people to join). and they may give fresh graduates Senior Titles. comparable good benefit as they have no stock package, but be careful that they may change your target bonus on the 11th month of the current year. Life balance could be very good depends on which team you are in and which manager you work for.
Cons
Very typical Korean company. Very poor management. The management think they can abuse people and system as long as they pay the money. Very silly culture. People pretend that they are working on some project "real" with "real" customers, only because they dare not to show that they are not capable at all to the HQ. Most of the experienced and good people already left. the company has acquired several companies in the past. They paid a lot but don't care about keeping talented people at all. Two things you need to learn if you were not a Korean: 1) speak Korean, 2) do smoke.