The only overwhelmingly positive part of this drama is the FL's fun characterization, which Park Shin Hye clearly had a blast bringing to life. In the early episodes this was enough to carry the show, but as the episodes went by the increasingly declining plot with all the asspulls & absolutely insane sequence of events made it very difficult for me to keep enjoying the drama.
Boredom is also a problem, I for one did not enjoy that every other episode had 10 minutes worth of torture scenes/fillers. All the procedural parts were on the boring side as well.

There is not that much romance in this show, but what there is it's really not working for me, the chemistry is not there & the whole romantic plot feels incredibly forced.

As I said before the plot is crazy, but it's not like they suddenly piss off the viewers with something really annoying, it's more of a perpetual eye rolling situation.

As for why is a show that's just barely hitting mediocre so successful? I think similar to Squid Game the audience that is normally watching regular kdramas found all the action scenes & bloodletting a new-ish experience that's still different -in my mind far worse- than now aging American shows of this type. -\_(ツ)_/¯