What a beautiful story. The plot is similar to back to the future in terms of time traveling and the parents being involved in the purpose of the travel. For me it's a great plot and I love how the k-drama develop it.
I would have loved a final episode a little be longer explaining how the parents meet again, and how different was the protagonist's mother life, but well it let us to imagine those parts.
It's a k-drama that sometimes I will revisit.