Before I get into the cons of this drama, I'll lead with the pros.

One - both lead and supporting actors did brilliant jobs. In that department at least there was nothing lacking, especially the three leads.

I went in blind without reading any reviews, so I don't know if this is a popular or unpopular opinion, but in mine, at least, SSR stole the show. Might be a bit biased - I've always had a thing for slightly unhinged, jaded anti-hero types who go just far enough that they're still toeing the moral line without outright crossing it, and he played the Jayden role to a T, making him my favourite character in the show. All the more so because of SSR's amazing acting. So forgive me for going into a bit of a character study here.

I'm not a very ends-justify-means person, but he was just righteous enough, although underhanded and manipulative, that it made him all the more appealing as a character, with the hidden truths and character development that made me love him all the more, right up to the very last scene with him in it. I was a bit dissatisfied by his (rightly deserved) ending simply because I found myself rooting for him despite my best instincts. But again, that bit of righteousness in his choices brought him his deserved ending so who am I to complain?

I also really loved Yoona as a character (though the acting felt a bit lacking). A competent, independent woman who refused to be defined by and lean on the powerful men in her life, who didn't allow her ambition to take shortcuts with her job or interfere with the ethics of her decisions as a medical researcher - I wish she'd gotten more screen time, and a happy ending with the person she loved.

Two - the remarkable attention to detail. While I personally have neither medical knowledge nor knowledge regarding Korean law, it seemed to me that the research was well done with respect to both. Especially since they went so much in depth with all the on screen surgeries. If anyone here has medical knowledge to correct me, then feel free, I'm quite curious how accurate it actually was. But that isn't the extent of attention to detail - when you pay attention, you end up noticing a lot of small details regarding behaviours and situations that add a certain realistic depth to the plot that is easy to overlook, and easier not bother usually because people don't pay that much attention. I wouldn't be able to give examples without spoilerizing so I won't.

Three - revenge. I've not come across a satisfyingly done revenge plot that I didn't end up loving, though I have come across those that left me completely dissatisfied with their open (admittedly more realistic) endings where things aren't quite resolved and the revenge didn't quite manage to come through after "The End". In that aspect this one was as satisfying as could be, cathartic in a way only a truly good revenge plot can be, with all the moments of truth spectacularly dealt.

Now cons - holy shit, was this show was a slow starter. And by that I mean slow enough that it took me about five months - seriously - to get through the first two episodes. Considering the one-third-episode-long surgical scenes that wouldn't make much sense to me anyway since I have no medical knowledge to appreciate his (projected) genius, all of that should have been completely skippable, but I couldn't even skip them because of how important they were plot-wise. That and that time spent (probably another third of the episode) on character development for a character who, you know from the premise, is going to die within the next twenty minutes. Especially considering that one-third-episode-long surgery was on the very same character, who, minor spoiler, will be dead about five short minutes later real-time (and a day later inside the show?). Knowing that from the premise, it took me a lot of patience to get through the tragedy, so I kept getting distracted by other things whenever I tried to start watching this show - about five months, maybe a bit more.

The second issue (sort of a continuation of the first, really) - the number of on-screen surgeries going on throughout the entirety of the show, and the amount of time spent witnessing them. As I said earlier, without medical knowledge to understand the importance of what was happening, all it did was bore me and make me lose patience.

Third was the makjang-level of dramatics from some of the plot - so ridiculous that I found it a little hard to believe it could possibly happen in real life, starting from the premise itself. While it was interesting to watch regardless, and was good if I could shelve the logical side of my brain, I found it rather hard to believe that anyone would be able to get away with digging out a live person's heart and killing people left, right, and centre. Also, I understand that Koreans are obsessed with appearances, but is it so bad that a mother would make her five-year-old daughter undergo painful plastic surgery? I'm not Korean, so I don't know what the extent of possibility is for that, but as an outsider at least, it seems horribly outlandish to me.

All in all, I loved it despite all the things I found annoying, and I definitely do think it was worth watching.