Secret Garden and Boys Over Flowers. Coffee Prince was another, but I didn't drop it since it was my first Korean drama (came from Japanese dramas) and I pushed myself to continue.

A number of very popular series don't interest me at all so I didn't even bother picking them up. And there are definitely some popular Japanese dramas I dropped as well.

the first two dramas that came to my mind were Secret Garden and Boys over Flowers. Secret Garden ruined the female character and the plot turned illogical. BOF was bad in every way. many liked it because it was like a train wreck that you can't stop watching.  I wasn't one of them.

Strong Woman Do Bong Soon

Goblin

Doctors

Pinocchio 

Goblin 

Moonlight drawn by clouds 

playful kiss

Heirs...coffee prince

Bride of the Century
Cruel City
I Need Romance 3
Liar Game
Secret Garden
Secret Love Affair
Suspicious Partner
Playful Kiss
Uncontrollably Fond

It's not even like I hate most dramas; I've just come across the wrong ones and finished most of them, haha.

either dropped/too hyped/just dont like em

The Bride of Haebaek 

You Who Came from the Stars

You're Beautiful

Descendants of the sun

I didn't necessarily hate these, i either dropped them or thought they rec'd more hype than deserved

  • The Boss and Me
  • Drinking Solo
  • Hwarang
  • Gentleman's Dignity
  • All versions of a Playful Kiss
  • Lovers in Paris
  • Please Come Back Mister
  • Saimdang Light's Diary

Kill Me, Heal Me

Uncontrollably Fond

The Bride of Habaek

Boys Over Flowers

Reply 1988

Hwarang

Shut Up Flower Boy Band

The Legend of the Blue Sea

Weightlifting Fairy Kim Bok Joo

W

Cinderella and Four Knights

1. CITY HUNTER

for me the series wasnt much special there were many good parts but overall i dint like it much.

2.ETERNAL LOVE

the series felt endlessly pulled long...for my taste

3.Iljimae

I really think  Pinocchio is too much overrated....

The Bride of Habaek is the worst drama i ever have seen.

Hate:

The Heirs, Playful Kiss (horrible message of female submission, annoying romance)

Kind of hate due to incomprehensible popularity:

Goblin, W- two worlds (promising and then a mess)

Didn't like it as much as the others/Pretty average:

Doctors
My fair lady- 2009
Goong
She was pretty
Strong woman do bong soon (funny but just that)
Cinderella and 4 knights
Legend of the blue sea (the girl was a frustrating and lost puppy)
Secret Garden
Bromance