Plots:
Season 1 was intense. Each episode kept me on my toes. It was super stressful and as much as wanted to drop it to avoid the stress, I couldn't. Season 2 was also very interesting and showed us the unsuccessful revenge story. Season 3 was a bit rushed. The writers threw all the history and motivations into it. Although it was quite interesting, some things did not make sense. For example, Logan coming back to life. It is literally impossible for a bomb to explode right next to you and for you to survive. I hated how they kept making everything worse for Bae Ro Na. Killing her mum was enough. I am quite thankful Logan was alive though and that Seok Hoon and Ro Na got their happy ending.
Acting:
The acting could not get any better, Joo Dan Tae and Cheon Seo Jin's acting literally blew my mind considering their real personalities and roles in other dramas.
Rewatch value:
I personally would not rewatch the series only because of the amount of stress it gave me. It was way to evil.

So yeah, In conclusion, it wasn't bad, just a little rushed. It was quite interesting and I would definitely recommend it. Also, the sets, architecture and interior design were amazing. I would definitely recommend the drama if your looking for inspiration for that kind of stuff