Rating: 4.5/5
As the name implies, it is a prototype that was never released. This ROM is also listed in the Beta Games section. It appears to be test code written for the initial stage of the game. Having been an original Gameboy owner, its a shame they never developed and released this game. Looks like it would have been awesome back in the day when Diablo was big.
You also need an emulator to run this game. To grab one quickly, please check out our GB emulators section.