There is so much to say. First of all, for those who watched the series first and learned about the existence of the manga later, things may seem like a everyting was wrapped up so quickly (You are right.). The story of Yul and In Seo has been slightly changed here, there is not much depth. (sorry, the manga has achieved a much more successful weave in this regard.)
Although the main lines are faithful to the manga, there are some things missing. And of course, 80chapter can only be summarized as a 20-minute series with 8 episodes, so I won't dwell on it too much, but I can't help but say that I hope there will be a special or season 2 because Yee Chan's military service and his personal development afterwards and Yul's Seoul life in the music industry are not in the series.
The choice of actors is very successful, they reduced Ye Chan's excesses in the manga and they did it very well (the TV series is more successful than the Manga in this regard), Yul loses his tough stance very often... (the actor's laughs very cute :) Nevermind, I can ignore this too.
In general terms Drama was good acually better then good. They needed to add more chapters or they needed to be longer episodes but cute, lovely and love the chemistry between actors. Music was well enough.