Music, that when heard, makes you want to play the game or relive the memories.
With modern audio, stock music can be thrown in easily, and it will sound decent and give the "epic" or cinematic feel the game designers want. But you often don't get memorable themes and relentless catchy melodies.
That said, there is some great composition in modern games. The Halo series is an obvious mention, with several memorable orchestral and piano pieces. Indie games often get closer to the composition style of the older video games you mentioned.
I do agree that the Halo music is pretty good and memorable (especially the whole chanting monk deal).
Every experience is so raw as a child, due to having had so few of them at that point. Therefore the memories feel more vivid.