itscelina :
You Who Came from the Stars!
This was one of the first Kdramas that I watched and despite being from 2014 (I usually watch dramas from 2016+) I thought that the romance was so sweet and adorable and I couldn't stop watching! Apart from the romance the mystery was quite good along with the secondary characters (And the secondary couple!).
Also, I see that you are currently watching 'Its Okay Not to Be Okay', if you love Kim Soo Hyun's acting there I think you should watch YWCFTS as it is definitely one of his best dramas :)
Yes it does seem like a lot of people like it! That's funny, I also usually only do more recent dramas (2015 is around my cut off)! And yes, I am loving Kim Soo Hyun which got me thinking I might check out You Who Came from the Stars.
So there is a secondary couple and not a love triangle??? Thank god!
I also don't like strictly romance usually so if there is a mystery element to the story too that sounds great.
Thank you for your rec!