This drama mostly revolves around the emotional rides of the lead roles. Their emotional ups and downs are main plots for the drama. And all this ups and downs have been shown mostly in a comic way. It's like a cheerful journey with confusions. All the characters have some sort of comic sense which will refresh you throughout the drama.
As for the antagonists, their character was not extreme. There were no big tragedy or hectic extreme evil content in the drama. As this drama has only 18 episodes , they did not include unnecessary tragedies. They stick to the main story all the time. I was little lost in episode 1, but from episode 2 you will in which direction the drama is moving, and they did not change their direction till episode 18.
In terms of acting, this drama is next to best. Ji Sung has played a very interesting character as main lead. He will definitely make you laugh hard. Choi Kang Hee played the independent and strong girl No Eun Seol. She is very mature and considerate, while Ji Sung's characterCha Ji Heon is very immature and impulsive. This North pole vs South pole contrast in their character makes the drama as lively as it can get. You will want more of them to watch.
The side characters are included in the main story. They are very closely related to main story, their story is integrated to the main leads' story. So you will find interest in side characters' scene as much as main leads' scenes.
Music is the best in this drama. bgm and the theme song are really refreshing and energetic.

IN SUMMERY ,
If you are thinking of having some light chilled out time with romance and comedy, this is the drama for you.
THE ROMANCE WILL MAKE YOU FEEL LITTLE OVERWHELMING
THE EMOTIONAL CONTENT WILL MAKE YOU CRY A LITTLE
BUT THE COMEDY WILL MAKE YOU LAUGH SO HARD
AND THE FRIENDLINESS WILL GIVE YOU A LOT OF COMFORT