TLDR; generally a good drama, but does have a somewhat repetitive plot. not your typical fantasy drama in that it's a little more insightful. don't expect anything earth-shatteringly good, but it is still a worthy watch (in my opinion; this may depend on your tastes -- watch the first 2-3 episodes to get a taste)

story: it's not horrible, but it does feel extremely repetitive. for the main leads' story, it is a repeat of angst and pain at not being able to be together, and then happy times, and then it goes back to the idea of "suffering is inevitable". when I was watching some of the scenes, I was like, "Haven't I already seen this before"? the second couple/love triangle story line is messy as well and honestly problematic at times. however, I did like the contrast of these two stories--1 more angsty, heavy line for the main leads and 1 more "typical" first love love triangle.

cast: this was hands down THE BEST PART of the show. thank you to whoever casted these people.
all of the actors and actresses were great at their roles!! and the chemistry between the couples (especially PBY and SIG) was sooooo chef's kiss. the visuals also. damn.

music: c'mon. we've gotten Ailee, Baekhyun, and TXT. what more can you ask for?

rewatch value: this one's low because it'd be a drama I'd rewatch if I had absolutely nothing to watch. I don't think it deserves a rewatch by itself, but if I was bored out of my mind, the plot is interesting enough that I would watch it again.