Sky Castle is definitely worth watching. Most k-dramas revolve around romance but this drama was on another level. This drama will give you a vibe that other k-dramas haven't delivered.
In my eyes, the villain character was Han Suh-jin, the mother of Kang yeh suh. Of her hesitations and greed, the whole scenario was a mess. She hesitantly but deliberately supported Coach Kim even though she knows what was wrong. Because of her greedy and immoral moves, the situation in the drama was complete chaos. If she just told her husband about hye na at the last moment that kid could live.
Overall, the drama was great. However, the hero of this drama was Lee soo im, the Mother of woo jo in my eyes. She was portraying an ideal mom.