I hope you'd give Shopping King Louis another chance. You'll be laughing and heart-warmed all along. :)
Legend of the Blue Sea
The K2: For Song Yoon Ah's sake. Only her acting matters, the rest is illusion!! (besides Ji Chang Wook's abs :3 )
I can't tell you to give anything a second chance since I've also dropped some of those dramas lol
Since @pamn has a total of 4 dramas in oh and ptw I can't tell much
Give W-Two Worlds a second chance
Well It started so good. But began to hill down in a few episodes. Pity really it seemed like it was going to be a awesome drama.

Honestly I felt our tastes are very similar. I couldn't blame you for most of drops.
Descendants of the Sun - It's the only one i can recommend with clear conscience. Nothing mind blowing but a great military - medical hybrid. It has a solid main lead and a awesome second couple i rooted for them so much. No love triangles and minimal nationalism. You should definitely finish it.
The K2 - Story is very meh. Female lead is so flat. Ji Chang Wook and Second female lead is great. I watched and liked it only because of them.
Hwarang - It really felt like a historical school drama. I liked Go Ah Ra but chemistry with the main lead was off. There is mission arc around episode 15. That is the best part you should at least watch this 2-3 episodes.
I'll start "Kill Me, Heal Me" today and i only see people praising this drama. Give it a 2nd chance!
Winter Sonata, really nice drama!
Cinderella and Four Knights: It was a pretty cute drama. I wasn't a huge fan of the main girl, but the three guys are great! I would give it a chance if you are looking for a pure romance drama.

Shopping King Louis: I would highly recommend to rewatch this if you are in the mood for a romantic comedy. It was a pretty good show and it was funny.

The K2: If you are a Ji Chang Wook fan, then you would not want to miss this. The story was meh but intense at the same time. I liked it.

Hope it helps!

Suspicious Partner, same reasoning you gave for K2 - kind of lol... it's JCW.
Bring It On, Ghost: Uhm, it is a really cute drama. The chemistry is bomb tho. I really enjoyed this drama. 

Fated To Love You: I really like the story and it is also very funny. Planning to re-watch it in some other time. :)