1st & 2nd season - Love it! 5 stars.
3RD SEASON - 3 stars: The change in characters, especially Yoo-Shin, really killed the vibe. You can tell this season had different directors. The way the season was directed (recorded) was not as good as the first two seasons. Some of the scenes gave the old style vibe because the way it was recorded (ie angles) and the music. For example, season 3, episode 5 at 27 minutes and 17 seconds when Ga-bin threw a flower vase at Dong-ma. The Dong-mas replacement yelled a lot, which doesn't match the original Dong-ma character in season 1 & 2.
If there is a 4th season, I probably won't watch it unless they bring back the original cast.