First of all the most positive things I can say about this drama is the acting of Kim Bum and Lee Dong Wool.
Now lets start the review:
The first 4 episodes are the best. You will love them, they will keep your curiosity and you will like be the characters (not all maybe). But after these, episode 5-6 are the most boring and really bad episodes, they are like filler to this drama. After these the ride for the enjoyment is up and down. Some episodes are good and some are bad.

The romance between the leads is best in the starting episodes then it becomes cringe. You will see yourself fast forwarding their scenes together. They have chemistry sometimes and sometimes there is none.

As for acting,
Lee Ding Wook is did a good job not great. This role suits him. He is cunning and humourous.
Bo Ah, Not a fan of her acting and never was. Her she did a good job in few episodes. But her acting is cringe sometimes. She is not suitable for the romance here or maybe the writing is poor.
Kim Bum, Never saw him before, this is my first drama of his. He is the shining star here. You are gonna love his acting.
Side Characters also did a very well job.

Overall it is not a bad drama. The writing could've been a lot better.