The drama was wonderful at first, it was entertaining and it was painful to have to wait until the next episode.

The chemistry between the actors was great, as well as the aesthetic. However it wasn't enough to save the drama in the end.

The plot became lame and uninteresting after the two lead settled in their happy life and the revenge against the villain seemed to be forgotten.

As much as Do Do Hee and Gu Wong's sweet and funny moments were a delight to watch at first, it turned to a tasteless comedy that didn't bring anything special anymore because it didn't relieved the stress of the episodes as it did at the beginning.
Speaking of comedy relief, the gang could have been a nice touch but it was under used and didn't live up to its potential.

About the villain : it was interesting to search clues on his identities at first but the last couple of episodes made him mediocre, I doubt he will leave a long lasting impression on the kdrama's villains' book

The plot really went downhill after the episode centered on Gu Won's past life, as interesting it might have been, it broke the pace of the story and starting episode 13, it only went worse.

Episode 14 : unnecessary breakup, and the fact that Gu Won killed Do Hee's parents didn't actually brought much to the plot, especially so late in the story

Episode 15 : bad and disappointing

Episode 16 : also disappointing

It seems like the story and its characters lost their sparks and became of shadow of what they could have been