I was planning to watch it for several months and I regret hesitating cause it's truly a masterpiece. 
- The story is really interesting. There's two major parts so you won't be bored if you don't like slow-paced shows. MC always had a clear goal and always achieved it.
- The actors are astonishing. Everyone really suits their roles.
- The friendship. It goes so deep, there's so many levels to it and all those levels are gonna break you heart and you gonna love it.
-I enjoyed the fight scenes a lot! It might be not pleasant for some people but i think you know what you doing starting this show. Once again it's really satisfying to watch them fighting.

The first week after watching this I cried just cause of seeing some weak hero clips.
So to sum up I'm in love and totally gonna rewatch this show.
P.S.: DO NOT read the webtoon. It's a totally different story and you might get obsessed cause it's awesome.