Yes, I always play games with the volume on. The music makes a difference.

Not really important to me, but if the music is really terrible then it brings down the entire game for me.

 This confuses me. To me, it's the directly opposite.

I can't think of any game with terrible music. So most games have just decent music. Then, I don't notice it. Then there's a few that have awesome music. That brings the quality up like hell. But music hardly brings it down for me.

Care to list a game with terrible music (that isn't terrible overall).

Super Mario galaxy and Mario kart wii. I always put my sound very low when I play those games.
The soundtrack when you had to fight Bowser was the only one I liked.
But I know many people like the music in SMG, I just hate it(It's my opinion, I'm not saying it's a fact or anything). Another thing I hate about SMG is the terrible voice acting(It has very little voice acting, but sometimes Rosalina or Mario speak like thank you or stuff like that). Rosalina sounds like a girl who wants to kill herself, lifeless....

Metroid prime1,2 and 3 have very good music in it.

World of Goo anyone?

World of Goo's music is awesome. Was gonna say that yesterday but I was lying down and was too lazy to type it.

@Samas Aran i would say your ears are broken for not liking Mario Galaxy's tunes but then you like Prime's music so i am confused.

Extremely important.

When it comes to video game music, to me, it doesn't matter if it's an 8-bit, 16-bit, 32-bit, 64-bit, 128-bit, orchastrated or even from an artist soundtrack! If it has a catchy tune that will burn into your brain that will pop-up from time to time, sets the right mood in a given moment in a game that makes it a very memorial that will come back to you when you are in similar situation in real life or even when you find it to be aspiring composure! So yes, a purely simple answer.

also, I just played MadWorld with music at 0, still good since it has commentartor, but anyone can tel that it's missing something.

You're right... Well, it's not 90%. 

Fire emblems, Super Mario Galaxy and the Zeldas are almost all 66% or more remakes.

Same with Pokemon.

Same with Mario Kart.

Same with Super Smash Bros.

But that doesn't stop any of them from having some bloody amazing music. This is in line's with (what I believe) is part of Nintendo's philosophy.

The new game is the old game, with a small amount of new stuff added. In prinscipe, this would mean that the sequel would always be an improvement over its predecessor.