The color palette wasn't dim, developers just used the darker colors more frequently.
Yes, the Genesis has bright colors to chose from. The problem is, that when you need more than two
or three shades of a color, to make a nicely shaded object... then you quickly run out of options.
I do not know the memory constraints, and the colors per sprite limits... which also limit what a
developer can do in-game... vs in a Demo. With a demo, for example.. you can devote 100%
of a systems resources to making a certain effect. With a game... you have to balance the systems
resources... between sound, graphics, and program logic.
A Genesis Demo could also feature nothing but a full cartridge worth of sampled speech / music..
at quite a shocking level of quality. However, again... the developers were not going to have CD
quality samples, because then they would not have enough room in the game carts for decent
graphics to be stored as well.
As any decent artists knows... there are many tricks you can use to get around certain limitations.
In the case of your SF picture, you can see the use of Dithering (alternating patterns), to help create
the illusion of an in-between color shade.
In your examples of both Sonic and Super Mario games... these are more in line with "Cartoon"
flat-shading. Meaning... they are mostly large single color fills, that do not have much shading.
When looking at other side by side comparisons... it becomes clear that the limits of color
shades that they have to chose from, greatly effects the end results of the final picture.
Because the Gen lacks as many "Browns", you will notice that the books are very different in their shading.
The Gen version has to use more dark shades, because it does not have as many lighter shades available.
(or at very least, it cant afford to use as many shades, due to the shared tileset color and memory limits)
And since the shading ends up having a much greater Contrast level... they likely chose that darker
blue as the background, to better match the overall darker brown shades "average".
The better the Artist... the more likely they can make something look extremely well, despite the limits
of the system. Case in point: Earthworm Jim. I was never a fan of the game, due to the clunky control...
but the graphics are on a whole other level... compared to most typical console games. They were
drawn by very high level, traditionally trained artists.. and it shows.
The SNES would be able to simulate anything the Genesis did via FM Synth samples. It wouldn't be identical but it would be serviceable.
Thats simply not true. Listen to this song from Thunderforce II:
Most especially, note the sweeping of the sounds. Its one thing to sample a single note.. but its very different to
try to represent complex dynamic sound sweeping. Its one reason why Simulated electric guitar, rarely sounds good at all.
Target Earth (Skip to 10:46 (Song title = Surprise)
There are a number of even more complex musical pieces in both of those games, that never could be duplicated
on the SNES.
The SNES is more like a generic Midi sound. It was FAR easier for standard musicians to make music with it...
but it cant even come close to the complex and breathtaking sounds and compositions possible, with an FM synth like
the Genesis's chip.
In fact, many Genesis games have Horrible audio... because the people whom they chose to create music and
sound effects for their games... could not really utilize the FM synth properly. However... those that DID know
how to use it... produced absolute ICONIC Masterpieces.
EDIT: I Noticed that you said "Genesis FM SAMPLES"
The Genesis chip is "FM SYNTHESIS" NOT "SAMPLES". To make sound with an FM Synthesizer, you need to
program Mathematical Algorithms. While the chip also allows the playback of actual recorded samples... the majority of the music and
sound effects, were hand-programmed, with custom made Algorithms. This not only saved massive amounts of memory space...
but FM Synth sounds can be FAR more dynamic and powerful, than any "Sample Player". In fact... a lot of music that has samples in it.. were sampled from true Synthesizers.
As for my top Gen games... the ones that immediately pop to mind are:
Thunderforce II (IMO - Far superior to the rest of the series, and my fav. shump of all time)
Target Earth (Insane Arcade level difficulty, great story, great music, unusually creative gameplay elements. A real masterpiece of work)
Castle of Illusion
Strider
Ghouls and Ghosts
The Revenge of Shinobi
Rocket Knight Adventures (Admittedly, this one got a bit too difficult near the end for younger me, so Ive yet to fully beat it)
Zany Golf (Not a powerhouse game.. just creative, fun, funny, challenging)
These are the games that I could easily play over and over and over again... without getting bored of them.
As said, I owned about 50 games... but I never played the others more than a single beating.
There are other games that probably could make the list, that I never played (or only played a few min worth
on an emulator).