I'm glad you like it.
The graphics effect uses a render texture to render the lower resolution in Unity while still working on higher resolution computers. This render texture has no smoothing or anything, keeping the pixels sharp. For the models themselves you'll need a toon shader. The fewer colours that show up the better, as gradients look super weird.
I went around and created my own toon shader using examples found around the web. These techniques combine give a really nice effect, of a low resolution world, that still feels somewhat detailed. I was still experimenting with it during the jam, and I don't think low-poly is the best for it. I think it works best with surprisingly detailed meshes, and normal maps, but the textures of the images have to be fairly sharp, using minimal anti-aliasing. Aliasing is what we want.
I'm glad you enjoyed it though.