It's an rather impressive attempt to bring a doom-like game to the A500 with 1 MB. Considering the hardware it runs on, it's quite amazing. But to be clear, it does miss some features compared to Doom and well... It's an A500 so don't expect 35FPS
There's a massive thread about it (including several videos showing off game play and the progress of the project) here:
http://eab.abime.net/showthread.php?t=98654