Mine was shinning inheritance
Boys over flower. Although many people critics this drama,  this drama still have a special place in my heart. Lee min ho is my first bias !!!
Boys Over Flowers was my first K-Drama, and I was hooked after that.  I still really enjoy rewatching it.
I blame it all on Stairway to Heaven. 
Still super new to k-dramas so... my very first is Reply 1988! This series made me laugh and even cry so much ( I was just expecting a cute love story), and the messages about family, friends, and youth is just genuine and hit close to home (anyone can relate to at least one family/character in the series). I love the 80s particularly because there were so many good love songs! I have been watching as much k-dramas as I can (even though I have to focus on my studies as well LOL).
mine was love rain ,,watched with my gf..
My first Kdrama was Playful Kiss ????
Flower Boy Ramen Shop :)
I don't really remember about my very first drama, but the first drama that left quite an impact which led me to kdramas was Queen Seon-duk.
I can't quite remember if it was Coffee Prince or Princess Hours. I always want to say the latter though.
She Was Pretty. I watched a couple of kdramas prior to that, but they never got me hooked.