Oh! Let me try!

It's the melody that we associate most with a piece of music. It's the aspect that is the easiest to remember. Pop-music is quite melody centric, I think. Older video game music is like pop-music. It's very memorable and we become attached to it, which is why we like to hear it outside of the game.

Newer video game music is more like film music. It's less noticeable, but still improves the experience a lot. The function of the music is to support the overall experience, not distract from it, or to be likeable on its own.