Goodbye is the 2nd track from SNSD's fourth extended play (or mini album) entitled Mr. Mr.
The track starts with a groovy beat which reminds you of a Detective Conan episode (see how weird I associate songs with anime soundtracks?) and then an incredibly twist takes place as the catchy opening perks up into an infectiously gleeful chorus and then more bubblegum awesomeness follows.
The first time I heard the song (although it's a cliche of some sort), I fell in love with it. And then I saw myself uncontrollably clicking the replay button again and again.
It is nostalgic in a very light and positive way. Whenever I listen to the song it reminds me of a sunny day or a laid-back afternoon getting lazy and snugly in my room with my closest friends. It is a happy-sounding track despite the message of the song which is obviously about the good in every goodbye.