I just downloaded the SuperTux data files, and, yeah, that's a huge quantity
of images.
I can see now: the problem is that the SuperTux team used blur (they should
have sticked with flats).
What's interesting though is that at a small size (like for a portable
console),
the game looks pro, maybe with a non transparent high contrast text
background for better readability.
Perfect example: see that igloo in the intro? In classic pixel art, it would
look infinitely better.
I was comparing with mario 1 to 3 designs, all the shadows are simple flats.
I think it looks better.
Hey, maybe a trick is to mass-modify all the files to push them to a lower
res with imagemagic, thus maybe giving them a nice pixel effect.
Actually I just tried the GIMP pixelize filter.
It can look better, but it doesn't eliminate that blurred look completely.