[From a 20-year-experienced Korean drama series audience here]:
This is my first time writing a review publicly cos I feel the poor rating doesn't give this drama a justice. And I also can't seem to understand why it receives this low rating either. I've watched hundreds of K-drama series, and I went through an awful lots of various emotions through watching each one of them. I bumped into this K-drama accidentally when I didn't know where to watch, and after reading its plot, I decided to give it a try. Little did I expect that it'd get me so hooked.
Similar to other life-and-death-content K-drama series, it made me cherish my everyday life more and spend more time to care about my family members and those loved ones around me. There were some episodes which made me cry my heart out like a baby. The mysterious cliff hangers at the end of each episode will also leave you at the edge of your seats. On another note, most of the main characters have their own respective pasts which are the explanation of their identities in the series, and the cinematography is also amazingly done.
Overall, this is one of the best K-drama series I've ever watched. Despite the low ratings, I really hope those who are still reluctant will give this drama a shot and watch it. Seriously, this drama shall deserve more ratings considering a lot of hard work and efforts which were put into its production.