The executive summary here is that there was too much sadness and trauma for too long for the final payoff. I don't like series that give you happy only in the last 10 minutes or some such. This series did that

Others have written excellent reviews, as usual, so I'll just put a few points out there to perhaps help folks decide if this is their cup of tea.

The Good
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- The acting!

Ra Mi Ran is great as the mother, although the role was really annoying to watch.

The twins were, as everyone said, adorable.

Ahn Sun Jin was fantastic, We watched this series because of her, after seeing her in Hospital Playlist.

- The few, and unfortunately only a few, funny moments were done well.

The Not So Good
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- As noted, too sad for too long. We needed more of the happy times with Mi-Joo and Kong-Ho after the trauma was (mostly) resolved.

- Not enough Ms. Ahn! She is great and we did not see enough of her in this series.

- Something about Young-soon's mourning was just off. I can't place my finger on it, but that scene just did not work.

- The side characters were too over the top. For a very serious series, they may have wanted some comic relief , but it was often out of place.

Recommendation
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This is actually hard to recommend, which really bums me out. But if you are looking to being bummed for the great majority of the series, and need a big dose of sadness, this may be for you