Both dramas revolve around a crime and a small child that witnessed that crime. Both kid's father was convicted for that murder. Both kids grow up and become police officers that try to make up for what their parent did. Both fight for the right way in the police field. Both end up investigating cases that resemble the case of their fathers. Both find out that there is more to the case.
Both have an element of a past crime or case returning to the present to haunt those who were involved in what may have been a cover up within the criminal justice system. Watcher's incident is from 15 years ago where is Chimera's is from 25 years ago -- with police officers and others working against the clock to to uncover the truth and root out corruption and injustice.
Both leads are very similar when it comes to their character and both dramas are in general having a lot of similarities as well. Both deal about leads that suffered a devastating loss in their childhood, and both got shaped because of that. Both became police officers due to that and both are faced with a crime that hits very close to home.
Both dramas began airing at nearly the same time and both dramas have quite a lot of similarities. For one we have characters that lost family members and we have cases and people that have something to do with that. We have twisted characters that one, especially in watcher, can't declare as good or evil. Both dramas have very strong female leads . Also, both dramas leave you hanging at the edge of your seat, waiting anxiously what will happen next.
A mysterious detective partner duo, teaming up with a strong female lead. Corruption, cases being not what they seem to be, and police officers making mistakes. All are both themes in both dramas. So far, however, The Good Detective seems like the little sister to Watcher. If you enjoy The Good Detective you will adore Watcher.