The aesthetic is intentionally low-fi. They’re rendered using a retro technique called sprite stacking, where you take 2D image slices and stack them vertically in pseudo-3D space. An explanation is here: https://medium.com/@avsnoopy/beginners-guide-to-sprite-stack...
The examples in your link look much better than anything on the SpriteStack page; probably because they are rendered at a higher resolution, as the parent poster suggested.
It looks like the examples are rendered very, very small and enlarged for display. Here's the rabbit; it is only 25x23 pixels.
https://spritestack.io/apng/default/889?v=15698873450001
They would look much better if the same model was rendered at a higher 2d resolution.
I am not using spritestacking as a mean to render things since a long time. It's intentionally sharp, low res and non antialiased because that's the style I like in games.
Please check media on my twitter to get a notion of how it really looks like right now https://twitter.com/rezoner/media
Also there doesn’t seem to be any anti-aliasing applied which would be a bare minimum here. Anyone have a good idea why the webmaster made these choices?