This Drama's MAJOR Plus points:
1. Its MUSIC.
It's mind blowing. All the songs whether they're Sad songs, Title song or Background music.
2. THE CHARACTER OF EUN HA WON:
Very optimistic and real. No over acting. No beauty concepts. We get inspired just by looking at her genuine smile, her hardworking nature and her dignity.
3. Love Isn't Fast:
The love story seems Very real because there's no rush. Love is built slowly so viewers find it quite logical for protagonists to fall in love so naturally. We smile throughout the series while watching these love scenes. Funny scenes as well as emotional scenes make us drentched into the series and the actors'acting.

MAJOR FLAWS:
1. Lack of Focus.
Whenever A good drama is judged, it has the same focus from the start till the end, so the viewer doesn't get bored. But, This drama didn't have a focus. In the start, the focus was on the "So called missions" of Eun Ha Won (female lead) who tries so hard JUST to complete those missions. Then suddenly the focus is shifted to the love story of Eun Ha Won, with the boys in the sky house. The missions are left As they are. Why? It seems unreasonable.
2. WRONG NAME:
I don't know what made the writer to give this story the name CINDERELLA AND FOUR KNIGHTS? There're only three boys in the sky house, fourth one had nothing to do with being her lover or something. Even in these three boys, only two are given a chance of being her lovers and among the two of them, one wasn't given enough time to convey his thoughts about his love (despite being worthy) just because the writer doesn't want. The story doesn't match the name AT ALL.

If you want something lovely and cute, watch it.