Enjoyable.
That said, first - the irritations with this drama
I found the pacing too slow. This should have been absolutely no more than 16 episodes at most. I think it actively spoils a good drama when they spin it out with unnecessary pauses in dialogue. No body speaks that slowly! Perhaps they "think" that it heightens tension, but it ruins it.
The music was heavy handed to say the least. It's not BAD music. It simply tries to maximise tension or convey emotions which should rest in the writing, or the production - it's a real indicator of laziness or poor work when this happens. I suppose there may be times when it is used to supplement poor acting, but never have I ever seen that!
The plotting is pretty loose, with plot holes and poor depiction of - for example - realistic procedures to take down a conglomerate; recover from a coma; complete a medical degree; kidnap someone; arrest the entire board of a multi million company; and so many more!
The ML here doesn't do it for me. He's believable up to a point - especially in his role as underdog but brilliant surgeon moonlighting on the shady side of the tracks, but I don't believe him as a romantic lead. For some reason his screen presence in those moments just isn't strong enough, and - even though he pities the FL - I just do not see any chemistry.
The FL here also has little to work with, but perhaps does her best. Unfortunately she spends most of the time immobile and expressionless, and then when she is recovered and has her own agency is revealed as a very unlikeable person. I didn't believe she deserved anyone's affection. Pity, yes, but warmth, not so much. When she was with Tae Hyun, she seemed like a different person, but she was unfortunately not someone I would trust for a moment - her first instinct would always be brutal revenge. TH was absolutely right to get out when he did, but when they get back together, would I trust her to be changed? not much. Her vengeful patterns are rooted in her background and her anger, but we hear about incidents when she was incredibly young and that adults around her feared her revenge - that's never going to change. She might never take out her anger on TH - but she will in a heartbeat hurt anyone else around him - and that would break his heart. Also - is the fault with the writing or the actor - I find it hard to say that another actress could have presented a less imbalanced personality - I think the writer failed to get the balance right.
All that being understood - what's to like
I was engaged by some of the relationships as they developed, especially between Tae Hyun and ... nearly everybody else. He starts off being someone who seems to have very questionable morals, but little by little that gloss is peeled away and we see him as someone prepared to take risks to protect anyone he loves: not perfect, but an enormously high achiever; bruised by life, but not yet beaten down; possessing a drive for excellence wherever he places his hand; increasingly able to empathise and very quickly form alliances wherever he finds himself, with the most unlikely people.
There are several moments of satisfying victory - both in the hospital settings, the mansion, and the company world. Each are pretty unrealistic, but still enjoyable.
There are a number of thought provoking issues, moral dilemmas, real risks, psychological struggles and personal conflicts, as well as genuinely heart-breaking moments. Many of the last are (for me) ruined by very heavy handling from the director, and the liberal serving of heavy strings in what I can only refer to as foreground music, but if I were reading it on a page, they would be very moving indeed.
The plotting is not well balanced. There's a massive shift in focus from hospital settings to conglomerates, with huge focus on indicators of status and power, and ways in which those both affect the world but can also be undermined. It's a roller-coaster -and sometimes annoying, but some of those elements are very interesting.= and make the rather chaotic plotline bearable.
The acting was competent all round, with some very familiar faces which always mean good things - notably Jung Woong In, Kim Mi Kyung and Oh Na Ra in minor roles - not much screen time but always a lot of dramatic punch. Chae Jung An was excellent as the female airhead who hides a knife-like mind and enormous determination - and a very dark and vengeful personality. Her husband, the main villain was serviceably presented by Jo Hyun Jae - handsome and affable in appearance, a certain amount of charisma, but perhaps not quite enough, but believable as the boss with murderous capacity. He did a very good job in making the character, apparently strong, but in reality easily manipulated by his Secretary, very believable. The secretary, played by Choi Byung Mo, was (for me) always very obviously the real villain, so I had no surprises when his conspiracy with all the other baddies was revealed. That could have been handled better, but it was all flagged so desperately obviously in the script and direction that I can't for a minute blame the actor.
I apologise for this long and rambling "review". It was hard to get to grips with my thoughts. This somewhat reflects the pretty chaotic plotting of the drama though, so perhaps not so inappropriate!