The only complaint I have is about the constant reuse of the same song in every episode - it's a good song, but by the end of the show I was like, "Do I ever actually want to hear this song again?" That said, I love the song(s?) that Rachael Yamagata contributed to the soundtrack. All in all, music was one of this show's strengths.
The acting and the 'realism' of the story was the other thing I loved most about it (same goes for the other show I just finished watching by this director, Something in the Rain, which I ADORED). Obviously it was a sweet romance, but unlike some K-dramas out there, it was a little more realistic in the sense that it shows more what everyday Koreans may go through as part of their dating lives (I say this as a non-Korean who is no expert on the culture/typical lifestyles).
I can certainly see myself watching this show again, however it was fairly slow moving, and if you're into more action packed dramas, this one may not be for you. If you're into character-driven, realistic and relatable dramas about everyday Koreans (oh, and a beautiful leading man), then I'd certainly recommend it.