It seems a little like cheating to put modern microcontrollers inside the cartridge that do all the heavy lifting. At what point are you basically just using the game boy's screen connected to a much more powerful external computer? It would be like me creating a new "SNES game" with a raspberry pi stuffed inside the cartridge with GPIOs mapped to the SNES cartridge interface and saying "there oughta be a full 3d SNES game" but at that point the SNES is doing very little processing compared to the pi's SoC which is doing 100% of the 3d rendering.
All that said, this project is still pretty sweet and I enjoyed the writeup.
All that said, this project is still pretty sweet and I enjoyed the writeup.