It's pretty much boring for me. I almost gave up after the first 12 minutes of ep.1 but saw a lot of early comments about how great this drama is with just the first ep so I watched it till the episode end, but this is all I'd give my time for this series. It officially is a dropped project for me.

****Edited 2: Due to quite a fuss about I dropped the drama and left my opinion only after "one" episode, I changed my mind to give myself and the drama some more chance and watched the 2nd episode. Anyway I still feel the same. Following is my original opinion without any edit. I reaffirm it without change.****

Brief opinion on some aspects:

Story: The plot is cliche, ordinary, guessable. The progress is very slow. Most part of the first ep is to give the background story - this background story has nothing new for the audience, just another same old kind of plot. The drama starts with the scene in the present before going back to tell the past story, so I kinda see how the story will become, not a difficult story to guess the storyline.

Character design: Simple and plain. The bad side is bad. The protagonist side is simply straightforward. There won't be the so-called character development in this story even though the time span is almost 10 years. The kids might grow up, be stronger and start to love each other, but it's just a straight-line walk. No interesting conflict. Just some revenge.

Acting: I like both actress and actor who play the main characters, but they can't make me feel along the characters with their acting esp. Ji Soo - this isn't the best version of the character he plays. The mother role that Kim So Hyun plays isn't portrayed that well either. She may be too young for that role.

Scene: For the CG part - it's not the best CG though acceptable. The shooting location in the nature is refreshing for a nature lover like me.

Music: Just so-so. Not much comment. It's not bad to be noticeable.

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Edited 1:
There're some fusses both on the comment sections of my review and of the drama itself over why some people already gave their review with the score only after 1 ep. Below is the reason on my part that I replied to one of those comments:-

I gave a review b/c this already a finished project for me. I drop it. It is done. I want to take a note to remind myself why I drop it and how much I (don't) prefer it - that's how the review comes.

In my opinion, the way Mydramalist designs the type of data to collect is quite good now, like scores from those who complete and drop the dramas. In the future when there's enough data accumulated to analyze deeper, they will surely categorize and show the result in more scrutinizing way. Just that people have to input data as detailed as possible for that to happen. You wouldn't feel much grumpy about the reviews from those who drop the drama if you understand data science.

Below I leave a link to another opinion about the way to collect data on the site and how to make use of them in case you're interested:
https://mydramalist.com/discussions/suggestions/28529-make-impossible-to-rate-uncompleted-dramas?pid=962745&page=6#p962745

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Interesting link about dropping a drama:
https://mydramalist.com/article/dropping-asian-dramas-is-ok-054182455