Well, it's obvious for everyone that Do Jin Woo is the worst part about this drama, every second Jin Woo appeared on screen it felt revolting. In fact, you may include Jin Woo and Seol Ah plot line as a whole in general. I highly doubt anyway would like Seol Ah ending. Looking at what the writer did to Jin Woo and Seol Ah plot line and looking at her previous works, I'm starting to see a pattern. Is it safe to assume it's a reflection of her own life?

It's not like the drama didn't have other problems. The drama was interesting for the first few episodes prior to the 9-years time skip, it gave off promising vibes with good build up then became utterly soulless, monotone and even got hit with a massive downgrade in overall quality. Maybe about 90% of the drama was uneventful, things kept going in circles with little to zero progression.
The writing was straight up bad and inconsistent. Some parts you can notice the writer is trying to create some logic but most of the time the writer end up doing the exact opposite. Most of the side stories were weak due to the lack of investment in liking any character, since none of them stands out anyway. This also made the size of the cast feel smaller than it is.

The ending as well was flat, lukewarm and lacked a meaningful conclusion to any character.
Chung Ah and Joon Hwi ending was too quick, while the other characters got a "whatever bs" kind of ending. It's really a shame what this drama ended up being since the beginning was too good, a massive bait and switch tactic.

If you can't stand single digit IQ characters then you should avoid this drama.
2.5/10