the only drama I have awarded a 10/10 rating to is misaeng. I feel like I am constantly holding out for that near-perfect or just extraordinarily good drama, so most dramas I watch end up somewhere between the 7 & 8.5 range---I don't even have a single 9/10 drama (yet).
So far only The Lover but once I finish Six Flying Dragons I'll rate it 10/10 ;^)
A Gentleman's Dignity 
Soredemo, Ikite Yuku : Great casts. Show 2 point of view (villain's family and victim's family). Frustrate you like you're one of them. Sakamoto Yuji!
It's okay thats love!
Out of 114 dramas, I've got 9 dramas on my list that I gave a 10:

Nine Times Time Travel (k-drama): impossible to stop watching, must see what happens next, how is he going to make everything right, and will they finally be together?! 

Hana Yori Dango (j-drama) Well, it was one of the first dramas I watched and the fist time I LOVED a drama (even though I knew it was a guilty pleasure), it was the drama that made me a drama addict... 

Orange Days (j-drama): So heart-warming and special, one of my dearest dramas with characters you can't help but love

Gunshi Kanbei (j-drama): 50 episodes historical drama, it could have been twice as long and I wouldn't have been bored, so many wonderful characters that you love and care about as if they're real, great acting from everyone!!

Beethoven Virus (k-drama): I really, really loved it with all my heart. Good music, great acting and great chemistry and a love triangle that isn't even annoying because all three have this great chemistry! 

Iki mo dekinai natsu (j-drama): Very interesting and special drama with intense emotions and forbidden love between the lines!

Kimi wa petto (j-drama): Cute and heartwarming, a female lead I felt so close to and good chemistry. A bit silly at times perhaps, but also one of my early watches and I still remember it fondly. 

Koukou kyoushi (j-drama) A very special drama with a unique and pretty bizarre plot, my heart almost ached because it was soooo good in a strange way!

Nirvana in Fire (c-drama): Simply the best drama I have watched! Everything about it was so captivating, from the costumes to the intelligence of the main character to the relationships between the characters, good and bad ones. It's an unforgettable drama!
I've only given one drama a 10, Signal. Even though I was thinking to give it maybe a 9 or 9,5 since I felt the ending was kind of rushed. But I loved the drama so incredibly much and is probably one of the best works I've ever seen!
I have only given out two perfect 10s: Weightlifting Fairy Kim Joo and Reply 1988. I have read mixed reviews on both, but IMO, these two dramas executed everything wonderfully. The case, plot, script, acting, cinematography, OST, etc were all on point. A perfect 10 from me means that I enjoyed it a lot, but that doesn't mean everyone liked it. I don't think there is such a thing as a 'perfect' drama, but there are dramas that we absolutely loved. 

Comrades. For me this is a perfect drama. From the acting, directing, plot and story... Perfect