Agree. I hated them together. The age difference bothered me. Incompatible Couple: Lee Min Ho and Go Hye Sun. just no.
Agreed. He is WAY to old for her. Old enough to be her dad...creepy couple. Song Victoria and Chen Calvin (when love walked in)
Lee Min Ho and Kim Hee Sun
Disagree. I think they were actually ok . Kim Myung Min and Lee Ji-ah in beethovens virus
Yeah he was a little old for her. I couldn't even finish that drama

Yoo Ah In and Kim Hee Ah

I know it was noona romance but I just could not feel the chemistry between these two leads and to me this drama was ultimately very dreadful to watch.
Agree.

 Yoon Shi Yoon and Kim Sae Ron in "Witch in the mirror" 

Besides the age gap, I didn't find any chemistry at all 
AGREE! I just couldnt handle the romance line between them, so I stopped watching the drama.
Jang Na Ra and So In Guk in I remmember you... Even though I like both of them, they just didnt work for me together.
Agree!!

Lee Jin Wook and Jo Yoon Hee in Nine.
Agree, kisses were great but that was it for me. 

Lee Jong Suk and Jin Se Yeon in Doctor stranger
Agree! I liked the pair of  LJS and KSR better. :)

Yoo Seung Ho and Park Min Young in Remember - War of the Son, maybe because it wasn't the focus of the story. 
Agree! They were noona-dongsaeng (sibling relationship) than a couple. I never felt the chemistry between them.

Park Shin Hye and Lee Min Ho in The Heirs....while everyone loved them, I never felt their chemistry (maybe not enjoying the drama much is also a factor too lol)
AGREE! ....Oh my goodness, I didn't enjoy the drama at all. But in the fleeting moments I did, I had MAJOR second-lead syndrome.

This is a suuuuper unpopular opinion but..... Shin Min Ah and So Ji Sub in Oh My Venus; I was super disappointed and thought their chemistry was really off.
Disagree, I thought they had great chemistry.

Jang Hyuk and Jang Na Ra in Fated To Love You. Second lead (Choi Jin Hyuk) was much more compatible with her.
Disagree,  I thought they were great together

Lee Joon Gi and Nam Sang Mi in Joseon Gunman.
Agree, especially since they've worked together in a previous hit project before. 

Lee Seung Gi and Go Ara in You're All Surrounded