You just got a new game. You tear the game out of its box, sit your ass cross-legged on the floor while you slam the game into your SNES. Maybe you have a brother or a friend with you, you tell him you just got a sweet new 2-player game and you wanna play together.
The intro shines on. Oooh, ahhh. The start screen. In your childlike excitement you frantically hit the start button until you're playing the game. The screen fades to black, and fades back in and you see Kirby. And the music just screams "You're beginning a huge and exciting adventure."
The first level's music has to be really gripping, because this paves the road for the rest of the game's music...And atmosphere.