I think this drama proves that when it comes to looks we can all be quite shallow, so suspend beliefs and prejudices and enjoy.

Handsome male lead dates girls purely on their looks and in a very short time (average 2 months) realises their personality is not attractive enough to continue so drops them.
Our FL has never measured up to society's standards of good looking and in her youth was bullied and teased (she assumes) for her looks so has low confidence in this area.
Set the scene for the beautiful ML to be the model for her art class and she becomes in lust for him.

The fantasy of her wearing a ring that cloaks her real appearance allows her the chance to experience an adorable guy being devoted to her. The fact that no one else can see her transformation is the twist. She luckily stays true to her own personality, probably, because she realises this is a temporary transformation and not likely to last. ML finds that her unaffected personality is very attractive and falls deeply in love.

I liked the tension of when she is exposed but not the execution. The 2FL is also given some sympathy as her backstory is revealed.
The ML is also shown as vulnerable due to his relationship to his mother. The FL is the luckiest because she has very loving parents who are good role models for love.
The story is entertaining and as a fantasy drama it works well.