This drama was awesome. I watched a scene accidentally in Instagram and inmediately got interested about this drama. --The acting skills of the cast are good.
--All the characters are likeable:
I always have a problem with the lead female character of any kdrama. I find them very annoying or clumsy or
childish -That's why I stopped watching "The Healer". Here, the female is perfect. On the other hand, I've always loved the cliche personality of the the lead male character - very cold and unsmiling. In "kill it", the protagonist plays this role on another level.
Note: You can definitely feel the chemistry between characters. That's better that kissing and hugging scenes.
The other characters are sweet and funny, but they don't lose the drama's tone.

--Fast development of the story: Unlike other people, I found the story very fluent. Everthing was revealed at the right point of the story, and the fact it was only 12 episodes long makes it easy to watch.

The OST: I haven't listened to a good OST since "The K2". It's excellent. It's the first time I like all the songs. Even though my native language is Spanish, I am trying to learn the lyrics. Then, if you don't want to watch "Kill it" because you have read negative reviews about it, at least listen to the OST. You won't regret it.

SUBTLE SPOILER:
--Right ending: The ending suits the story. Even though, it is not what we hope, it is what we expect.
Note: For our hopes, there is an extra scene that makes us feel satisfied and to some extend pleased with the drama.
My wish: I would love to watch another season even though I know it will be irrational to fix the ending. However, I won't be mad if they do it.

ADVICE:
If you are so used to romantic comedy. Then, I would recommend not to watch it, but please listen to the OST.