This is a Round Table post, but it's kind of late: I started out thinking about low-fi sounds and it spiraled away from me, with the result that it's more in line with January's topic (soundtracks) than February's (ambient sound). Sorry about that.
An NES sound chip has 5 channels, says Wikipedia. That's two pulse wave synths at set duty cycles with pitch bending, a triangle wave, a white noise generator, and a delta pulse-width modulation (PWM) synth capable of doubling as a crude 7-bit PCM sound channel. These capabilities are not particularly extravagant. The noise generator is primarily good for special effects and simulating snare rattles or cymbal hits. The PWM channel is also usually used for the bass half of the groovebox. That leaves three melodic channels--and not three polyphonic MIDI channels the way that most modern synthesizers understand, but three monophonic (single-note) instruments to carry the tune.
As a result, there wasn't a lot of variation in the "tone" of the NES from game to game. There were occasional attempts to broaden the palette--mimicking flutes by taking the triangle wave up a few octaves, for example, or the chimes from the now omni-present Final Fantasy theme--but for the most part the instrumentation was static. Imagine that every rock band had to use the exact same equipment for making music, and you have some idea of what this is like.
So it's honestly impressive, if you waste an afternoon listening to NSFs ripped from old Nintendo cartridges (who, me?), how very different a game could sound, and how much composers managed to do with such simplistic tools. Metroid and Mario may share the same hardware, but they are radically different soundtracks. The former embraces the artificial sounds produced by the NES chip. It broods like a Moog Mini that's just had its lunch money stolen.
Super Mario, on the other hand--well, here's the thing about Mario: it's a victim of its own success. We've heard it so many times, either through the game series or through the many pop-culture references, that we're a little dead to its charms. But listen again to it again, and really listen this time:
I mean, that is a genuinely funky theme. Hear how the noise channel isn't being used to emulate drums, but instead creates something more like beatboxing? That's a distinctly NES-friendly move, and it also sounds to me like it pulls inspiration directly from the contemporary hip-hop of the early 1980's. But note that the rest of the arrangement would easily fit onto a clavi or a piano, with the left hand starting out in unison with the right's chords, then wandering off into a laid-back bassline before returning. I don't think it's a stretch to hear a little Stevie Wonder in there (even more so in the slap-bass riff of World 1-2). Sure, when he plays it live nowadays, composer Koji Kondo adds a little swing. Still, this is a far cry from the "beeps and boops" stereotype of 8-bit music, a reputation that the platform hardly deserved (and was primarily assigned by people who had hardly ever really sat down to listen to a game).
These are songs that have really stuck in the heads of people my age, whether they were really hardcore gamers or not. They became a standard. When Belle picked up my copy of New Super Mario Bros., practically her first comment was that they never have managed to get the music right again. Which is a funny comment, since the music capabilities of the DS, while still primitive, are leaps and bounds better than the older games. So why the nostalgia? Why the feeling that the new wavetable interpretations of the songs are somehow less appealing?
I think part of it has to do with the instrumentation, for both the listener and the composer. For my parents' generation, Switched-On Bach may have been the first real experience with electronic music, but for Gen X and younger it was the NES that introduced us to synthesizer tones. And while they may be rough and low-fi, the NES chip's channels have a kind of pleasing weight to them--when I hear analog synth junkies rhapsodize about the sonic characteristics of a Moog or a Prophet 5, this is what comes to mind. I think you really have to understand the NES platform as an instrument with its own distinct sound, compared to today's sample-based consoles.
For composers on this bare-bones hardware, it was clearly a struggle to translate their traditional music chops to such a spare set of sounds. And many of them failed, leaving us with a legacy of generic techno music that lasts to this day. But the successes fused great songwriting onto a new palette, one that was as much defined by its constraints as by its capabilities. It forced the music to pull in new influences in order to overcome those limitations. I think you can hear the tension in the best examples of NES songwriting--that is, in those earworms that have stuck with us, and which become less exciting when they're allowed to stretch out on higher-fidelity platforms.
Who else wants to talk?
Another reason why this post is late is because initially I thought I'd already written a Round Table post about soundtracks: SKU'd Perspectives, which discussed P.N.03 and Jet Grind Radio, and how I want an action game with rhythm.