It is of course subjective and varies from game to game, but I do naturally consider music to be an important part of any video game. Perhaps as important as graphics and game play, even.
I would even go so far as to so that the quality music is part of what games like the Super Mario, Mega Man, Castlevania, Metroid, Sonic the Hedgehog, The Legend of Zelda, etc franchises timeless classics. (To name particularly notable, salient examples in my opinion.)
My nostalgia for such 8-and-16 bit games, and their MIDI scores, played throughout my formative years moreover clearly shaped my current tastes in music vis-a-vis my love for electro-industrial, chip tune, IDM, synth pop, and other such musical genres.