1 Six flying dragons
2 Empress ki
3 My love from the stars
1 heartstrings
2. pinocchio
3. The heirs
1. Signal
2. Special Affairs Team Ten
3. Coffee Pprince
1.healer
2.dots
3.moonlight drawn by the clouds
1) The Princess' Man
2) Kill me Heal me
3) Moon Lovers: Scarlet Heart Ryeo 
1. I Remember You
2. Reply 1988
3. Pinocchio
1- pinnocchio
2- kill me heal me
3- w world
1 Heartstrings
2 Love Rain
3 Boys over flowers 
Dong yi 
Boys over flowers 
Jewel in the palace 
1. Goblin
2. I Hear Your Voice
3. It's Okay, That's Love

what put these over the top for me were the realistic romances and an amazing OST.

...As of right now... ^.^
It's okay that's love
six flying dragons
empress ki

A good drama must have a) a great ,unpredictable plot b) superb acting and undeniable chemistry between main leads c) whatever else that makes me go WOW! Either OST, cinematography, directing etc
1 My Love from another start. ( what got me to into  watching kdrama and my all time fav )
2 Weightlifting Fairy Kim Bok Joo ( this was the cutest drama I ever watched, and I never had to skip any part)
3 My Girlfriend is a Nine-Tailed Fox ( I'm not sure why lol, but I love this drama. Ending was kids idk but still it make me smile a lot )

p.s. Not into historical drama.
1. Liar Game
2. Weightlifting Fairy Kim Bok Joo
3. The Lover

They're actually not very old dramas, but I was so caught up in them, while I was watching them that I had to place them high on my list!
Liar Game is simply amazing! I love love love the cast (Lee Sang Yoon
1. Descendants of the Sun
2. Moon Embracing the Sun
3. The Horse Doctor
A Gentleman's Dignity
Winter Sonata
Goblin / Phoenix