@ReadOnlyCat: The framerate target is a full 50 Hertz on a real PAL-Amiga at all times, the emulator (which is used in the video) has trouble syncing / keeping up. Good guess about the sprites - but no. Sprites are used for bullets and player ship only. The big objects could be more colorful than they are in the video. Maybe in the next iteration of the game version some things look different :-)
@Marcuz: Thanks a lot. Cheers have to go to Kevin Saunders and Adam Morton too for fabulous pixels and music. You might want to have a go at the game with some kind of emulator ...