It was both unrealistic and realistic at the same time.
It showed that everyone had a dark side and that some thrive just to get revenge, it even gave the lead roles a brand new perspective because they too were also brought into the world of reality as the script also showed their flaws and not pictured them as goody two-shoes.
However, how the characters chose to get back at the ones who have done them wrong was harsh, unsympathetic and not realistic. And how Seoul keeps going back to Jung and not minding what everyone else says about him is just pure garbage.
The characters were all simply unloveable (except In Ho) even if they were as realistic as possible. Usually people would be excited and thrilled at the fact that the leads would finally get their revenge but this was not the case, it made people hate them even more because their dose of revenge was more than what the antagonists bargained for.
All in all, this was a drama that is neither good or bad. I literally hated the leads though, hopefully they would rot together and live their lives as psychotic as they made them out to be.