Boys Over Flowers - I'm a huge fan of Hana Yori Dango anime and Tsukasa in particular, but Korean version made me want the female lead to end up with the second male lead, not to mention that I was either bored or annoyed through most of it. I didn't drop it only because I was watching it with somebody else.
Moon Lovers: Scarlet Heart Ryeo - I actually think it's a very good quality drama and was interested in the beginning, but the male lead started to get on my nerves at some point, so I dropped it. I feel weird though, because everybody loved it so much, literally never heard of anybody ever disliking it, so I'm partly thinking of picking it up again, just to see if things get better.