Geometry Wars/WMG

The player's ship is the sole remnant of a once-great space empire.

You're either going to seek help from a neighboring galaxy or simply trying to survive Everything Trying to Kill You.

The simple shapes of the Geoms evoke their Sinister Geometry

The geometric shapes are Eldritch Abominations whose mere appearance drives men insane.

You're the bad guy.

Maybe you just can't help spewing laser death, but the enemies are throwing theselves at you to stop you from destroying everyone else, even at the cost of their own lives. Perhaps you're given power-ups and lives by a cruel god.