Kim Hye Yoon absolutely brings it in this movie. I'm used too seeing her in lighter roles, so it was really cool to see her take on a role so opposite to her type cast. She nails it, taking the role and playing it perfectly.
The story is just so tragic and you really and truly feel for these characters. Watching the film play out, you feel Hye Young's rage and are able to understand her actions.
It's not a perfect film. There are a few plot points that are forgotten about and then come back at the end without reason. It's like the writers forgot that those characters were out there and felt the need to resolve that even though it wasn't really required. The rewatch value is low, mostly because it is so a tragic and depressing movie. It is meant to be, but I don't want to watch it again soon.
But make no mistake, this is a great movie and absolutely worth the watch.