Legal High 
Last Friends
MARS
Healer
I Hear Your Voice
Can only see 2 that you PTW. One i haven't seen the other is Heard it through the grapevine. I like it and would recommend it but really does depend on whether you like that type of story.
From your large PlanToWatch list I have only seen Liar Game (2014) which I highly recommend it , (its an amazing psychological game ) there is also the Japanese one which is better than the korean in term of the games and tricks , but the korean has a more dramatic feel to it

these others I haven't seen myself but they seem highly recommended and reviewed
Bad Guys
Ghost (2012)
Old Boy
Ouroboros
Two Weeks
Rich Man, Poor Woman (2012)
My Girl (2009)
You have so many to choose from, but your plan to watch list has so many good things!  First, my favorite drama ever, Bridal Mask, so I have to recommend that before anything else. 

My favorites of the rest (of the ones I've finished): White Christmas, Missing Noir M, Bad Guys and God's Quiz

And Nodame Cantabile, even though that's completely different from the others I've recommended.  I can totally recommend all of those dramas. If your taste is like mine, haha.
@zeamays' PTW list :

Brain
China Town
since you're already watching 3 dramas, I'll recommend some movies for you: The Man From Nowhere and Hwayi: A Monster Boy, they're amazing! I gave those respectively 9.5 and 8.5 :)

 @ajbcu + Past: thank you! I started watching The Master's Sun :)
on your ptw list you have 3 of my favorite dramas.. 

rooftop prince 
kill me heal me 
gu family book

you have to watch all of them but first you have to watch rooftop prince !!! i have seen this drama 3 times xD 
6 Persons Room
Twenty
Heartbreak Library
Beauty Inside & Mother :))
Bad Guys
Fated to Love You
Pinocchio
Blind
China Town - great cast.
Coffee Prince 
Dr. Frost- light psych crime
Oldboy
Liar Game- highly psychological
Oh my venus - adorable cast
@Spring

Coffee Prince - you would always see this mentioned when they talk about kdramas
God's Gift 14 Days - even if the ending is aish, i still love the episodes except for the ending
Incomplete Life - i guess you're already working. if you are, you would probably like this
Ouroboros - from your list that's from Japan, this i would recommend
The Man From Nowhere - one of the best Korean movies
@prettytin

In Time With You = probably one of the best TWdramas that I've ever watched that I still find myself rewatching it from time to time. It has a very simple plot and perhaps overused but the acting and cinematography are phenomenal!

MARS = I didn't love this as much as everyone else did but maybe because I was just scared most of the time in some of the episodes lol but I still think that you should give it a try. it's one of the TWdrama's classics!

You Are the Apple of My Eye = this  was a smash hit in the box office and it was based on a true story. Those facts alone can make one become curious and watch it right away (like I did! haha)

Material Queen = loved this because of the setting in Paris and because of Vanness Wu. Aside from that, the female lead here isn't common in dramas. She's super annoying but not the weak stereotype of female leads in dramas but it's her being ambitious that made her annoying but it was really fun to watch her!

Never Give Up, Dodo = you can finish this in one sitting because of the very short duration of each episode. Super funny, silly, and raunchy!

Present Perfect = a short Thai film that has pulled my heartstrings! Amazing plot twist :)
1 litre of tears - you need a box of tissue
house of flying daggers - classic
love me if you dare
ouroboros