A production which left a big impression on you  even after you finished?

It was Old Boy for me.I just couldnt more on from that movie for a legit week.

Shut up flower boy band for me, I watched it two years ago and I still think about it sometimes
Gaksital and Healer mostly ^^ 
Dramas: Cruel city, Mask, Healer, Good doctor, It's okay, that's love, Hana yori dango, King2Hearts.
Movies: A Werewolf Boy, Harmony, Sunny, Daisy.
There was many dramas that affected me in various ways that it was hard to forget for days...

SECRET with Ji Sung (phenomenal acting and writing - left me speechless for days) 
LIE TO ME (because of awesome chemistry between leads) 
HOTEL KING (that one made me marathoned it within 24 hrs - acting was insane! superb script and love sacrifices all the way - it was brilliant!)
HE WHO CAME FROM THE STARS (I cried crocodile tears at the end - never cried so hard in any drama at the end as that one)
SCENT OF A WOMAN (brilliant writing, and so many emotions few through me watching this)
BOSS & ME (simple gestures and romantic touches in that drama made goosebumps on my skin - it was so cute) 
THAT WINTER, THE WIND BLEW (such a sad drama but it really touched me deeply after watching it) 
CITY HUNTER (the plot was intense and the ending father-son love made me rewatch the scene 15 x at least)

.......... please note : HEALER and HEAL ME, KILL ME would have been on the list  but I have not finished watching these two yet. Half way at present right now.
Yea!  I am with green_tokki … Sorry, I Love You … and, I must add … Honesty/Truth (2000).
Korean movie 3-Iron blew me away, I was left speechless. Since then I have never seen a movie which left me with that kind of impact.
Nagareboshi, The Spring Day of My Life, King2Hearts, My Name is Kim Sam Soon, Ojakgyo Brothers, Prime Minister and I, Tatta Hitotsu no Koi.

Regardless of the ratings I gave these, they all stayed with me afterwards for various reasons.
"Amachan" , "Scarlet Heart" and "Gomen ne, Seishun!" 
Definitely White Christmas! It has been two weeks since I finished it and I still think about it 
Gunshi Kanbei (my heart is full of warm and fuzzy feelings whenever I see in the feeds that one of my friends is watching it)
Beethoven Virus (it's been over a year since I watched it)
Amachan (it's not that I think about it a lot but I miss it, and sometimes I find myself humming the opening theme or one of the songs...)
Iki mo dekinai natsu (I can't even explain why I loved it so much, I just did)
Koukou kyoushi 2003 (it was... intense)
Nine Times Time Travel (it gave me that feeling "I'll never like another drama this much again, can't happen!")
Roosevelt Game (same as above)
49 Days (surprisingly, since I expected it to be more easily forgotten)
Movie: Werewolf Boy - Completely took me by surprise, wasn't expecting such a story draw me in and never let me go.
Drama: Bridal Mask, King 2 Hearts, Shut Up Flower Boy Band, Secret, Cruel City
Movie: Old Boy - Left me slack-jawed for a a few minutes and it kept me thinking for days. No movie had left me that kind of impression. Though, it's not a movie for everyone, some may find it a little disgusting.
Drama: Healer , Good Doctor and You Who Came from the Stars
Koizora hit me hard but it was beautiful. I even read the actual story because I loved it so much.
Yuuki is another sad story that makes you realize how quickly your time can end.
I still think about Faith and God's Gift-14 days from time to time, wondering what I would do in their situation.