If you are planning to watch this on Netflix, stop now. Don't even waste your time. There are Korean series on Netflix that are way better, a million times better, than this series.
However, if you're the type who salivates on stupid decisions, slow-mo effects whenever they're introducing a good-looking person, characters who are somehow invisible to other characters even though they're just a few meters away, main characters choosing to die even though they and their allies have at least a minute to stop their killers, but they'd rather die so they can have emotional last words, etc. Yeah, watch it at your own risk.
Anyway, it's so bad, I almost destroyed my laptop.