Pros
The pay is pretty good.They will always pay you on time and honestly. They do your taxes for you (which are cheap in Korea.) Decent health insurance is provided, as is housing. If you like working with children this is great, and if you are teacher from your own country you can apply your skills and easily perform above expectations. Your school might take you in and treat you as family. You might have the chance to learn Korean. Working in a public school in Korea can also provide an opportunity to build professional skills, and experience multiculturalism from a unique perspective. For example, if you are a white male, when you come to Korea you have to learn to be the super-minority, which is similar to what minorities in American small communities experience all the time. Lessons like that are not available to most people and are an invaluable life experience.
Cons
It's all luck of the draw as far as what type of housing you get, the quality of your co-teacher/school relationship, how much free time you have, etc. Some people get a sweet deal and others get hell, and there is no way to anticipate which situation you will be places in. I was one of the lucky ones, but I now others who weren't. Also, living in a foreign country can take it's toll on you after several years.