This is a slow movie, with a very simple plot and storyline. I am a fan of the two main actors anyway, but I think they do a good job carrying the movie.
Are there flaws? Yes. But I would be nitpicking if I were to list them.
The main thing to take away from the movie, in my opinion, is honest and open communication. This is of course a familiar theme in Kdramas and movies; difficulties, misunderstanding, and conflicts due to holding back and not communicating clearly. It's difficult to "take a hint" if one isn't even being given.