People calling this song addictive... it so is. Reasons why I think so: the opening whistled melody 0:02-0:10 is of the "question-answer" type, with offbeat harmony from guitar. A very subtle (guitar?) countermelody @0:02-0:10 (something like F#-E#-F#-----, and F#-E------) that gets more complicated when the melody repeats again (such as @0:16 there's a guitar turn B-BAB-C#-D-C#, and @0:20 there's a guitar F#-A-B ornament). The little grace notes @0:04-0:06, reappear @0:25 (and many other places, along with the whistled melody, and I love it everytime they reappear!). The sung melody is of course very well crafted and memorable and indeed addictive.The drum riff the opens the song (and reappear @1:03). The "duelling" voices that first appear @1:06. @1:45 a more rhythmic/less melodic section (indeed the drum gets a more important role), which transitions to @2:05 a more sustained, "hymnal", more romantic sound. @2:10 countermelody starting with piano, and @2:16 the whistled melody comes back with variation @2:21. And @2:23-2:27 modulation to F#major, the first time in this song whose key is F#minor. The end of that phrase is "sipji aneun geol", meaning "don't want to", so one last desperate cry in the delusional major key before the F#minor comes back, with fiercer "duelling voices". Overall, there's lots of little new things added during repeats to keep the material fresh!