While this is a revenge plot, MC isnt fully insane like in Nidome no Yuusha, and actually still cares about the general public for the most part.
He has a clear distinction between just killing everyone who looks at him funny, and killing only who he needs to in order to get to those who are his targets. And usually the few "extras" are just as bad as his target.
People want a bloodthirsty psycopath for an MC, and he just isn't going to be one, which is usually why people dislike this story so much. MC and FMC are a good pair, both having similar circumstances, actually support each other, so that they don't go mentally insane with each of their revenge plots.
I will say that of everything I have read involving revenge, this story has some of the best methods of revenge. A lot of irony themed revenge, usually planned out in a way that is fitting for the target.