You mentioned it on our game page, but were definitely inspired by Obra Dinn's 1-bit technique. There were some really interesting tutorials on how that effect was achieved (e.g. https://www.youtube.com/watch?v=Ap4fXGTOb7I).
Here's a before and after with the shader applied. Real glad we didn't need to account for camera motion, as that would've made things a lot harder.