If you accept the premise of this series, it could very sweet.
Yes, Yuki's character may be a bit overplayed by the actress, but I think Tae-Oh is one of the most charming characters I've seen. He's so encouraging and adorable that I melt. It's perhaps a bit too unbelievable that he ends up as an intern at Yuki's workplace - but again, if you accept the premise and view this series as very light-hearted entertainment, it can work.
I really enjoyed watching this series and loved the inclusion of Korean language, culture, and since I know some Korean myself, it was fun to hear Tae-Oh's thoughts in Korean - especially when I don't understand a word of Japanese like the other characters speak in the series.
There are far too few series out there where the main character falls in love with someone from another culture - there should be more of that, and I think this series is a sweet little contribution to that.