If you haven’t played them already, you should really check out rRootage and Noiz2sa by ABA Games. They’re two variations on the shmup form, and the reductive visual style plays up the abstract nature of the genre.

But the really neat thing about these games (for the coders in the audience) is that the bullet patterns are not predetermined, but are instead generated using an engine that reads an XML document containing basic patterns, then combines them using a genetic crossover operation. The result is pure shmuppy goodness.

There are even Mac ports for those who swing that way, so no one has an excuse not to play these games.