I'm too lazy to write a long review, but I'm here to say that:
1) the best character of this whole story is Rang. I love his arch and the way his character develops through the story;
2) the ost is absolutely beautiful;
3) the most beautiful thing about this drama is the relationship between Rang and Yeon, and how it evolves throug out the episodes;
4) it's a good drama to just enjoy and learn a little about korean folklore (that's one of the reasons I started watching in the first place).

The story in general is intresting and keeps you wanting to watch the following episodes. If you just want to chill and watch a little of Dongwook and Kibum, this is a great opportunity to do it.