See below, originally gave 8 but had to update:
I am rating an 8 but may come back and re-evaluate after the series finishes. I was really impressed at the beginning 3 episodes, and the songs that were sung were just so Heavenly that it gave me the chills. Kim Min Kyu was unbelievable in the role and got hooked in those early episodes.
It's now episode 8 and kind of think it is getting a little hokey - with the devil and now he the ML Rembray is getting human feelings and can't act on them with being a Priest and all. Feel it is worth to keep watching and enjoy it for the fantasy drama that it is - and will see how it turns out. Am wondering how the ending will be since Remarry needs to get back and the real Idol needs to get home as well. Funny in lots of parts too.
FINAL RATING UPDATE: Sadly came back to reduce my original rating of a 9. Really enjoyed the early episodes, but for me the violence got to be too much and also the ending was so boring that I dozed off daydreaming and actually had to put it on again and fast forward to the end to see it again which now I know why I dozed off after seeing the ending for the 2nd time. Could have done better.