Free-talking classes are great if you have sufficiently fluent students. Your job is to start them talking and keep them going. Have them discuss the pros/cons of living in the city, vacationing on Jeju Island, going to school abroad, men doing more housework, the eternal struggle between Horde and Alliance, Terran and Zerg, whatever. Just keep them going. Set up a debate if you need more structure.
I'd love to do a class like this but my students aren't fluent enough. The closest I ever came was the one time I had to do a 90-minute conversation class with one student below sentence-forming level and no plan. I asked her about her daily schedule, her favorite subjects, what she does in her spare time, what she watches on TV, her favorite K-pop stars, what she studies at hagwon, what careers she likes, etc. With the help of her cellphone dictionary she was mostly able to communicate all this to me in laborious one- to three-word chunks. Because I kept the focus totally on her and filled every pause with another line of questioning I was able to keep her going for the whole 90.
So, if you try this sort of thing with a whole class, act as a facilitator: ask questions, focus on your students and follow the conversation wherever it goes. But again, it will only work if your students can communicate reasonably well and want to speak.