I was kinda disappointed by this drama. I did enjoy it. But I started it with high expectations, since everyone was constantly telling me how good it it, and sadly, I really don't see why everyone thinks it's such an incredible drama. I wasn't really into the plot at first, and my excitement sort of dwindled down after a while. I just wasn't able to get invested in it. I wish they had focused more on Young Shin and Jung Hoo's stories because the best part of this drama for me was the romance, it was really sweet. The action scenes were amazing, too. I enjoyed watching Healer's missions, I wish we had gotten to see more of his regular work as a night courier. I liked his interactions with the hacker ahjumma. Overall the story was pretty ok.

The enjoyment for me was mostly in the characters. I really liked Ji Chang Wook's character(in fact I liked him so much that I watched another one of his dramas after I finished Healer) Both Jung Hoo and Bong Soo were precious in every way (even if Bong Soo was just a facade). Park Min Young was great too. Young Shin was a great and dynamic female lead, and I enjoyed every moment she was on screen. Young Shin's dad was the best though. Him and his small gang of ex-convicts. The cast was quite good. What made me keep watching despite my lack of deep investment was Young Shin and Jung Hoo, they were both great individually and together.

The music was very nice. The OSTs were stuck in my head for quite a while. Plus they were in English, so I could sing along. Somehow, they managed to pull off English OSTs without making them sound as cringy as they often do in some kdramas, so kudos for that. The background music was fitting, too.

I don't think I'll watch this again. I rarely rewatch things and this has not given me any reason to consider watching it. (Edit 04/2020: Haha i did end up rewatching it (though i skipped a lot) because I wanted to see Ji Chang Wook again)

Overall I think this was a pretty ok drama, but not really anything special. I'm still a bit disappointed. I thought I was in for something mind-blowing because of all the great reviews on here. Plus it's just my type of drama, action-packed, suspenseful, dramatic... I'm not sure where it went wrong.
Watch it if you feel like it. The romance is wonderful, and the characters are well developed. It's not bad at all, I did enjoy it, but I just see it as another decent drama, not the masterpiece that everyone else seems to see.