Still one of the best, all these years later . . .

'Healer' himself is the key character to this story - the one who transforms from a loner, selfish, barely trusting anyone to a kinder, more generous person who wants to see justice done. His story would be transfixing on its own - but its paired with a believable romance with lots of interactions, a mystery with multiple subplots, and a moving story regarding old friends, family and generational hopes.

The acting is top notch, and all the leads (and many of the supporting characters) can go back and forth between humour, tragedy, action etc. with the drop a hat. The music is good enough. There is a lot of rewatch potential as a lot of its value is not in the 'mysteries' of the show.

I grade by other criteria as well:

Complex Themes -10
There are A LOT of themes here regarding corruption, power, love, friendship, selfishness v. sacrifice etc.
Character Growth -8.5
'Healer' grows a lot as noted above, and at certain points in the show does a 'Superman' type deception. Yeongsin does become a bit sharper, cynical and somewhat steelier over the show, but the majority of the transformation is on his side.
Nuanced Women -7.5
There are 3 great female roles in the show - very smart with strength of character, but unfortunately no real bond or connection between them until the very end. The women are more ideals and inspiration - motivations for the men in the show than fully fleshed out characters in and of themselves.
Cinematography/Production Values - 8.5
The action scenes are really well done on what appears to be a lower budget than what K-dramas have today. Lots of 'exteriors' shot in real settings scenes - good, basic cinematic camerawork. The main downfall is the wealthy people do not have the trappings/attitudes of the wealthy probably due to lack of budget.