The music is an important thing in all the "seventh art" creation. Some music can make a film really great (like Sergio Leone+Ennio Morricone western or the Rocky saga). For the VN is the same. The music must be appropriate to the moment, must emphasize, involve the player, It should not be thrown there randomly.
The ambient souds are also very important, more than the music itself. A VN without music or sounds is like a visual book, can be a good book but with music can be great!
Good music is hard to find, hard to fit and taste plays a lot too. Good ambience and sfx on other hand are much more forgiving. Silence can be a miss too.
Evermore for example you are in the correct mood before you start the game.
The right music at the right time can really help bring a game to life. Sadly thats a difficult thing to get right and a lot of devs don't manage it, but yeah generally some music is preferable to me sitting alone in dark late at night with only the occasional click of a mouse button or keyboard key for company.
Jesus that sounds more depressing than i meant it too
As long as it's not a shitty loop and you can tinker with the volume then yeah, games should have a soundtrack.
Feel the same about voices. If it's not some canned moans they took from a porn scene that constantly repeats itself during sex, then it can add so much to the whole experience. It's why I love when some devs go the extra mile and add some voice acting to their works.