It can be played with keyboard (left/right/space) or the right joystick (point & shoot).
My thanks to Sixxie for xroar, asm6809 & CyD and to Bosco for great ideas, inspiration and motivation.
In case anyone is wondering, it's all done in software, no hardware tricks and no speed up poke

Enjoy!

Edit: Attached version is now a bit easier to play and includes a vdk image