Speed by Shawn Hargreaves is a Space Invaders clone but with the twist that the 2d gameplay is projected onto four different pseudo-3d surfaces, which are at first viewed in alternation, but as you advance to the later levels will be displayed side by side, and finally all superimposed on the same display. This makes it extremely hard to see what is going on.

http://repo.openpandora.org/?page=detail&app=speed-speed-17506