Definitely worth a look but the minuses below spoil the impression.
As usual, events happen in the past and present between which there is nothing,
Oh no, Kim Soo Hyun growing up and was trained by the killer of his profession, ok.
But killer not just an murderer, it profession. and what he learned besides shooting skills and possession of a knife? seems like nothing useful.

As a result is a absurd ending and equally death
in principle, like his teacher with Alzheimer (no way without it)
But the storyline is logically completed-all bad guys are dead.
ps sorry for my english