I have watched hundreds of dramas, no joke. And although this one isn't new, there was a sweetness to it that I really enjoyed.
There were things I didn't like of course...the female lead's acting was meh...nothing to write home about. She had some scenes that I could imagine a more seasoned or nuanced actress handling with much more conviction. But the story was so well-written that it didn't even bother me that much.
Ji Soo was wonderful. He was able to take a character as simple and at first sort of annoying and by the second season, bring depth and maturity while not compromising his sweetness and authenticity. I have watched him other things and he really was able to embody this character well.
Jin-Young was also very very good. His character was really well-written. Usually second leads are so clearly non-contenders for the affection of the main female lead. The whole time, I started rooting for him, but when the pivot in the story happened, i could feel how he felt. I could understand the tensions he faced. I could understand so clearly why he and the female lead didn't choose him. I could feel his care, but I also appreciated his maturity.
I apprecitated the way the characters talked about their feelings and were clear and direct -- well, except the female lead....

The only thing I wasn't too crazy about was the pacing of the end...i wish they would have spent a little more time on some of the main couple and in flushing out the main female lead's character and feelings for the main lead.

But I still found my self very engaged and I definitely think i'll watch this again.