If you keep back issues of the Boston Globe calendar, you'll find a positive review of this restaurant located just south of the Porter Square station on Mass. Ave. The place is very small and the motherly owner is there to make sure you eat your entrees in the correct fashion. I ordered the bibim-bap, a dish with beef, rice, sprouts, and spinach, which came with a side of chili pepper sauce which the matron mixed in for me. The miso is recommended as well.
Seoul Food is definitely good. My only complaint is that they don't bring you enough of the side dishes (assorted pickled vegetables, bean sprouts, tofu, etc.) that I expect at good Korean restaurants. If you're in the area, I would also recommend the new Korean restaurant in Porter Exchange (behind the Gap). It's in the space where that macrobiotic vegetarian place used to be (the horror!). I recommend the soups, esp. Yuk-ge-jang, which is a beef-based soup with lots of chili powder. The owners are apparently from the southwest region of Korea, which has a unique regional cuisine.