I'm just finishing watching this drama once again. This is the third or fourth time in the years since it was made. What captures me the most about it is the three protagonists bonded together by a common struggle. Each of them is different, original, interesting, but they all have the same thing in common - the desire to protect the other two.
The mystery element in this drama is strong, clear, and truly mysterious. The plot twists and pressure points on the various suspects are well handled. The plot keeps you in suspense. The atmosphere has the right intensity.
I especially like the relationship between shamanism and Catholicism. They were presented in quite an interesting way. But the circumstances are also interesting.
But for me, as I mentioned before, the best and most important thing is the characters. Not just the main three. Each character is very believably drawn and portrayed. But of course the main three are the best.