I love revenge plots, especially in the hands of a highly intelligent and capable female protagonist but with the proper motivation, of course. And, there was no doubt that the people who made Moon Dong-eun's (Song Hye-kyo) life hell on earth were all more than deserving of the kind of old school, biblical vengeance reserved for the very wrathful God of the Old Testament.
And, actually, I thought that the series might have wanted to say something about the hot-button issue of school bullying and spousal abuse but opted instead (in typical K-Drama fashion) to focus on the obligatory fan service of a romantic pairing of the two leads with less than zero chemistry between them.
The level of gratuitous violence on display in both parts 1 & 2 felt unnecessary at times because the payback was nowhere equal to the damage inflicted on the victims.
Maybe if she would've exacted her revenge in the very gym where the majority of the bullying took place I would've felt more satisfied with the conclusion.