There are many, many different aspects of what makes a game, or even a general form of media, good. Since I'm busy this is all I had time to write about.
Music:
You want a memorable soundtrack, one that people will remember and actively want to listen to outside of the game. For instance, the creator of the music for the original Legend of Zelda is quoted as having listened to his music for hours on repeat, to make sure that it never got dull or annoying. And you can see it payed off, people still cover and listen to those songs today. I think a song should have these important factors
Immersive - The music should fit the level and give the level itself a feeling of life.
Doesn't get tiring - If you're stuck on a particularly hard level, you will be hearing certain songs on loop a lot, so the songs should not get annoying and tiring to the ear even after quite a while.
Isn't distracting - While the music should be good, it should not be so good and so loud, that it takes precedence over the game, and distracts from it.