Started out pretty decent, then amnesia hit and it all went to shit.
The problem wasn't just the stupid amnesia, the problem was that all creativity went out the window together with it. While amnesia plots are general just plain bad (out of more than 40 shows I watched with them, only 1 was a good plotline, and that later turned out the ML had faked his amnesia) this show just turns bad in general.
After the amnesia plotline hit the ONLY new content we had was the ML's sister and her lover getting together properly. Literally everything else was just rehashing the same problems, character traits and bahaviours again and again. Ml looses his Memory? Believes Chief Jo without any reliable person or proof to back her up. Looses his memory again? Believes Chief Jo without any proof to her statements at all.
ML looses his memory? FL doesn't even utter a single sentence to fight for the ML instead believing chief jo who has not a single shred of proof. ML looses his memory again? FL doesn't lift a single finger or utter a single word to fight for the ML...
It's honestly not so much that the amnesia is the problem, that could be overlookked (it's a Kdrama, they can't live without doing some tropes that are universally hated and siliked by the entire viewership in any country for some reason), it's that the quality is just gone. The writing turns from not-great-but-decent to something you'd get a failing grade in middle school for beeing so unimaginative, repetitive and just plain bad