Ikaruga (Dreamcast, GameCube)
Treasure's Dreamcast sequel to the legendary Radiant Silvergun was only released in Japan, althoughwe did get a GameCube version afew yearsago. Its black and white gameplay mechanic is pure hardcore. If your craft is black, you can absorb black bullets and destroy white enemies more easily. Switch to white and the opposite is true.
With the color switch activated at the tap of a button, waves of deathly monochromatic bullets suddenly become havens. Such polarized gameplay demands extreme concentration, but is also extremely rewarding. After a few minutes, though, you'll have to stop and actively remember to blink. It's that intense.