Since I'm not a good 2D artist (learning sloowly with low motivation but that's a different topic) here's what the current art process is:

1. Model a thing in Blender.
2. Render it in a low resolution.
3. Using ImageMagick apply a color palette.

The palette is I think the SNES palette that I took from Wikipedia and cropped a little bit.
There's a problem though, below is a screenshot of the game. Excuse the size :P.

It's extremely dark, I can't say if it can be passed off as just a "style" but it's even a bit hard on my eyes. And see the background, the black with green spots? That's supposed to be tall grass, but the palette reduces detail until it just looks like overly peppered lettuce.

The white rectangles will be ladder sprites, it's unfinished at the moment.

If you use rendered 3D models, why the palette constraint? That hardly ever looks good without much extra work, IMO.

Otherwise you could apply a cell shader in Blender to reduce the number of colors and get a more cartoony look. But then you'll still have a very limited palette and probably have to do a lot of color replacing.

I'm doing it like it was done for Donkey Kong: Country, which is why there's a palette.