It is for sure nothing you expect. And I am not sure if content rating is right, maybe 15+ would be better, I think that some younger will not really understand the story. Also it can be boring and times while plot is actually crazy/meaningfful.
What I love is how they mixed american (even some pretty big names as Jake Gyllenhall) and korean cast. I really like Choi Woo Shik here and Lily Collins.
Worth watching, even if you will not like it very much it is still worth seeing.