This series has only eight episodes, so when I completed two of them and realized that I am not even a little interested, I decided that it was time to drop it.

If I had to describe Once Again with one word, it would be slow. The characters walk and speak slowly. The plot progresses slowly. The episodes pass slowly.
The screentime could have been cut in half and no important scenes would have been lost. For instance, a substantial part of episode two shows what the viewers already saw in episode one.
The phlegmatic mood makes all the characters seem lifeless, like NPCs from a game. Kang Ji Hoon is the closest, in behavior and facial expressions, to being a real person. I liked him because he is kind. However, the script requires him to do things that do not make sense, such as taking a child to his dorm for the night despite knowing that the child's mother will come home in the morning and probably panic when she realizes that her son is missing.

Overall, although this series has an interesting premise and great OSTs, it suffers from bad execution.