Hi no worries about late reply, I havent checked this tread again until now anyways.
I don't really agree with the reviews that only the 1st 4 eps are good, I supscet those people simply don't like the melodramatic turn the drama takes at that point.
Cinderella's Sister is worth watching imo for the complex female lead's character journey.
Just a warning: The romance barely gets developed and only one kiss at last ep, but that's basically it lol. So don't watch it for the romance (even when FL & ML there are super cute together) but watch it for the FL, Her character there is very fenomonal!
FYI I did drop the drama at ep10, this is because annoyance over story not going anywhere (&hearing tgey dibt realky develop the romance either anyways), but even so, the character journey of ep 1-10 of the FL IS SO WORTH IT (despite me dropping the drama lol).
I might pick up the drama again & warch the rest one day when I have more time, but for now I'd say the 1st 10 episodes are easily 9/10 stars, so even if you end up dropping the drama as me, the first 10 eps are still very much worth it!!