Music is always at its full breath of expression; quality of delivery is the only aspect affected by hardware.
Limited color palettes and sizes are the same as limited sound channels and limited available instruments. They are no different: just as 'a tune' is good in midi form, an image, a reaction, is good in sprite or pixel form as well. You're tricking yourself if you're thinking that somehow it isn't. *
Visuals are absolutely limited by hardware; the inability to use, say, camera pans or zooming or dynamic lighting directly affect the way you can interwine the narrative in your visuals.
inability? you keep speaking of all these things as if they are absolutes, impossible: i don't think you understand what is and what is not possible in regards pixel art. You're acting as if the fact that things were done a specific way means it was not possible to do it any other way; this is a fallacy. It is possible to create relatively dynamic lighting in pixel art or 2D games - the issue being that it would be incredibly monotonous and time-consuming to do so, and there may be issues with memory depending on the console and the intended scope of the system. Camera pans are a matter of cinematography, not necessarily the same thing as the visuals themselves but rather a matter of the way these visuals progress.
Castlevania could have been "darker" (literally being darker is not the only, or even most important, element in whether or not something is "spooky" or "ominous") if it wanted to be, but it never chose to be: even on the NES.

the opening hall of Castlevania in Dracula's Curse. It's colors are bright and almost gaudy; but, I've replaced the colors with other colors from the NES palette. (nes palette:
http://doomlaser.com/images/nes-spec.gif )

It was technically possible, even on the NES; the more advanced the consoles became, the more capable they were of utilizing darker or more muted colors and yet Castlevania intentionally abstained from taking such a route:
because it was not the point.
I feel I should revisit a point I made in passing: "literally being darker is not the only, or even most important, element in whether or not something is "spooky" or "ominous". I should explain this - dark colors do not make something spooky or ominous, it is the way these colors are combined and the subject matter of the image in question.
http://www.pixeljoint.com/files/icons/full/metroid64.pnghttp://www.pixeljoint.com/files/icons/full/gbmock__r1177205021.pngthe first image uses the C64 palette (c64 palette:
http://www.wayofthepixel.net/pixelation/upload/features/05_arne/c64pal.png ), which has approximately 16 colors to choose from. Despite being slightly more muted than most palettes at the time, its colors are still fairly bright. But the image created above (created entirely within c64 specifications) still manages to create an uneasy, "spooky" and vaguely ominous atmosphere.
into account, you see that it's very hard to make a "dark" 2D image because being a piece of flat pixel art... it's flat.
...everything displayed on a monitor is innately flat; it doesn't matter if it's "rendered" in 3D, it's still nothing more than an illusion; an illusion which is perfectly capable of being copied with traditional art.

Here's another screenshot of Nosferatu for you to ponder over.
I honestly find most of the soundtrack to be sensibly worse than LoS - as in, miles behind.
Demon's Souls OST 06 - Phalanx If you say so~
*
http://www.pixeljoint.com/files/icons/full/dev0id_final.pnghttp://www.pixeljoint.com/files/icons/full/tyrion.gifhttp://www.pixeljoint.com/files/icons/full/wip42.pngthe first piece is c64 style, the second uses only 16 colors and the third uses 21 colors.