This game is a good version, and would have been an excellent 100% machine code game back around 1982. It fells like the re-fire mechanism is a little on the slow side, and it could do with a redefinable keys option. For the ZX81, my mind is trained to use 5,6,7 and 8 for directions, and 0 for fire. Though none of these are showstoppers, and it's easily a 4 star game.