During the Fall 2013 semester, I took three study abroad classes: Early Modern Korea and its Historical Sites in Seoul, Media Communication in Korea, and Korean (1). Overall, they were easy courses. Yonsei offers these courses so exchange students can have more free time. However, they are REALLY strict about attendance, so you start losing letter grades after a certain amount of absences/tardies. Just go to class, do the assignments, and you'll do fine.
Early Modern Korea and its Historical Sites in Seoul, taught by Kim Jae-Eun:
This was my second favorite class. It's a history class of course, but you get to go on 3 field trips throughout the semester. Albeit, they are field trips to places like Namsan Hanok Village places in Insadong, aka touristy places in Seoul, but I learned a lot of history that I wouldn't have learned on an average Seoul tour. Almost half of the total grade is based off 2-3 response papers to readings she gives out, since a lot of students aren't as fluent in English she doesn't grade on grammar but on the content. The other half of the grade comes from attendance, a group video project, and a final over the main points of the readings in class. The professor is really young and so nice, but her lectures can sound a bit monotonous at times.
This is the video project my group did for this class.
Media Communication in Korea, taught by Lee Young-Eum:
This class basically covers how the media was/is run and how it has influenced and changed Korea since the end of the Korean War until the present day. The content of her lectures is interesting, but her actual lectures are not. She's was biased and opinionated at times, her voice was monotonous, and sometimes she just read straight off her slides. The grade for this class was based off a midterm, final, and group presentation. The midterm and final were take home exams with a lot of mini-essay questions(all could be answered with her lecture slides plus personal opinions), and the group presentation was divided into 6-7 people so you only really had to do one slide of research. We watched a couple movies in this class and she bought us food twice. Before Chuseok, she gave a mini history lesson on the holiday and brought typical snack foods/drinks offered during Chuseok. For the last day of class SHE BOUGHT THE WHOLE CLASS PAPA JOHN'S! That's so expensive and she bought like 30 boxes for the 60ish students in the class.
Korean (1), taught by Jung Yeo-hoon:
This was my FAVORITE class. The professor was so nice and helpful. She makes sure everyone is ready to move on to the next lesson. This course is a beginner Korean class, so you start out by learning hangul and then move on to basic grammar and vocabulary. If you are completely new to Korean and don't want to spend 10 hours a week in the intensive KLI classes, then this is the class for you. The grade is based off many things since it's a language class, so even if you don't do so well on a quiz or homework you can make it up with other good grades.
I can only really speak from experience in classes under the College of Business, but if you plan on taking classes with regular Yonsei courses they will be very rigorous. No matter what class you take, expect many group projects and A LOT of readings!