This drama has so much reviews so I will get to the point.

Story:

I had high expectations from this drama since it's top rated but I wasn't that impressed by it,
The plot itself isn't that original- The man who has a job that it's the only thing that interests him,saves the girl and fall in love with her, reminded me City Hunter a bit...
The story as it goes by, is very good, everything is built in layers very well, especially the flashbacks of the past and the stories of the character's parents were really interesting and kept me wondering, also with knowing each piece of information as the episodes continue is very good, and I can say that it was made very well.
Some points I really liked and some things I thought were really predictable.

Characters/Cast/Acting;

I was a bit afraid of PMY at first because I remember her acting not that well in other dramas I saw with her but she proved that she can act, the other actors were good also and JCO was also very good (especially when he had to shoew emotions)
About the characters,
Healer and YS were nice, not that interesting but bareble to watch, I liked the master, the hyung and the ahjumma, hyung was the only character I could understand his motives and personallity, all of the characters were too much "black/white" they weren't that complicated and that's what bothered me ,they were only bad or good, Also there were also many characters that were insignificant like the detective, I felt that he was mented to be only becuase one scene in the last episode.
That Elder felt like a character that was invented to be a reason and not because he was necessary.
Moon Ho didn't have purpose in the story almost at all, I understand that he was like "a leader" or to connect Healer and YS to their past but other than that he was just "there" ,I couldn't understand him-why did he go againts his brother in the first place and what exactly his personality?
The only thing I liked about him was that he wasn't in love with YS ..
I liked Bong Soo, he was very funny and I enjoyed the scenes when he was there.

Music:

The good thing about the music is Ahjumma! I liked all of the songs she sang.
The main soundtrack (like the opening theme) was refreshing but for the fights scenes it wasn't always in the right place,
The other songs were drama-like and I don't think I will remember those.

Romance:

The thing I liked about the romance here was that even if they met an obstacle, they made it through and not like in other dramas "we can't be together because of-"
I liked some of their moments (some of them felt too much cheesy)...
I didn't understand why they felt in love actually, I can somehow understand why Healer-Bong Soo fell in love with her but she didn't have a reason and sometimes it felt a litlle too fast ,

Rewatch Value:

Probably not but the drama itself was indeed a good drama, I think that if it will be a "first drama" to someone he will really like it, but the reason I didn't give it a 10 was because everything there was predictable for me, I knew from the very start what's going to happen and how it will end,
Another reason was the characters and that's all, overall was a good drama.
I think that I was kind of disappointed because it is ranked so high, so I had high expectations .
I did enjoy it in some episodes; I wanted to know what will happen but I didn't enjoy it to the point that I would say that Healer is one of the best I've seen because it's not, and I know that most of you won't agree with me.