This was not a revenge drama. Instead, it is about a dysfunctional family at its core. People who are selfish, ruthless and place a good deal importance on ambition.
Gemma was one of the lamest female lead I have seen. All she did was act like a teenager with a temper tauntrum. While she ranted and raved about 'revenge', she was in many ways just like her selfish parents. She also didn't really get her revenge at all and others instead did the work. Along the way, everyone she used, including hopping into fake/real relationship with three men, were magically onboard with poor old Gemma and no one was angry with her. Even though she was like a bad hurricane that just created havoc with her emotional yo-yo, characters still felt for Gemma -- but most of the viewers did not.
The drama was weirdly watchable mainly because of the veteran actors who really essayed a couple who both hate and love each other. For some 30 odd years, their relationship status has been "complicated". The star of the drama ends up being a late entry -- stepson Ju Hyung -- who had some hilariously witty caustic lines.
So if you are looking to see a drama about a dysfunctional family tearing each other apart, secrets coming out after years and cold ruthless people finally getting broken -- this is your drama.
There were some interesting questions and themes but it never really got fully explored. The main point of the writer seems to be -- unbridled ambition and greed can be devastating and the chickens will come to roost even if years later. The choices you make may come back to haunt you years later. Anger leads to more anger and revenge just creates more revenge. Better if people just communicate.
So fair warning to anyone thinking of watching -- it starts off interesting and then.... you have no idea why keep watching.