if possible, give me your reason why u like that drama eventhough it got low rating in mydramalist.  Thanks
I honestly enjoyed the Heirs. I know people gave it a lot of hate and I see why, but I still thought it was really entertaining. I think part of the reason why I liked it is that I don't mind a constant push and pull love triangle and personally thought the 3 people involved in Heirs had ridiculous yet not boring dynamic. Sure, the drama was full of cliches and stuff, but that didn't bother me.
The suspicious housekeeper, goodbye mr black, 
Depends what is considered low, for me 7.5 and above is ok. 

So going by that my pick would be My Heart Twinkle Twinkle, but mainly the oldest sister's plot, I was so hooked and binge watched all 26 episodes in less that a week. The reason I loved it is because I have a thing for possessive and obsessive male leads and the one here has got to be the worst one out of all the Kdramas I've seen.
However the youngest sister's story made me want to throw my computer down the stairs it was so annoying and unnecessary in parts, so I have a love hate relationship with this drama.
The three dramas that I've got on my list that I've actually rated higher than the average by more than 1 point and that I rated at least 8:
Taereung National Village - I have no idea why this one is rated so low.  It's short, engaging, slice-of-life goodness.
Flowers For My Life - Excellent, funny, bittersweet, meaningful and pretty much free of cliches.
Tomorrow's Cantabile - Warm and sweet, lots of friendship warm fuzzies.  I liked it just as much as the Japanese drama version.

None of those are rated particularly low, all in the range of 6.9 to 7.8. 
I also agree about Goodbye Mr. Black....That drama is amazing..It had a beautiful love story,the female lead was badass and wasn't whining at all....Very good action,and twist and turns....I truly didn't understand why is was rated a 7.4-.-
Moorim School-I adored that drama as well....I suppose most people thought it was gonna be more about bromance than romance....The love triangle didn't make it any better I guess....I loved the romance part...I never really was a big fan of bromance to begin with xD.....It also had that Harry Potter vibe,so it was awesome to me
My Queen ... my 1st Taiwanese drama & 1 of my 1st noona dramas ;-)
Warm and Cozy, though I don't really consider it lowly rated.

Though I can understand why the rating is below 8.
Playful Kiss- It's my guilty pleasure drama. I don't know why I like it so much, I just do.
Moorim School- I loved the leads and I enjoyed the bromance 
King2Hearts- To me this deserves a solid 10. Every aspect of this drama was very well balanced.
Blood- Okay, I know why this got such a low rating, but despite the ending I enjoyed it very much. Although I do agree it could've been much better.
When a Man's in Love -  would be higher than the 6.8 if I influenced the rating alone!  I rated it a 9.5.  http://mydramalist.com/6063-when-a-mans-in-love
Mary Stayed Out All Night is rated pretty low but I watched it for Jang Geun Suk and ended up really liking it!!! I became a Moon/Mary fan as well!

Trust me, when it comes to rating, i always end up in different side than most people chose. Lol


HEIRS - a lot of people hated this, but to me, i can rewatch it a hundred times without getting bored!

THE LIAR AND HIS LOVER - at first, i hesitated watching this due to low rating and negative comments. Thankfully, i still watched this, and yep, love it so much!

MARY STAYED OUT ALL NIGHT - This also got me hooked and as a natural born hopeless romantic, this got my heart. 

Cinderellas Sister - i havent seen many melodramas so i cannot really compare it with others that are considered as "the best"in this genre but I personally enjoyed it and I was almost shocked to see it has 7.1 rating here

and I agree with Mary stayed out all night but i am not sure if i liked it because 'fake/pretend relationship' is my favourite trope :D