I'm pretty new to Kdrama but so far have found this to be one of my top three. If the lunacy and chaos of the setting and scenario doesn't pull you in straight away, then prepare for a lot if invested hours in the character dynamics and relationships.
To summarize...
Extremely well written.
Interesting and realistic characters.
Great balance of humour and drama.
Overall satisfaction.
This drama is 20 hours of your life well spent.