AstroShift unlockable arcade game
I love arcades, and spent a lot of the 80's in them.
As a cool bonus in AstroShift, I added an unlockable arcade machine in an arcade, with an arcade-y version of the game to play.
I added scanlines and ghosting to all the sprites in it, and lined the back walls of the arcade screen with other machines, running their attract sequences.
Did I mention I love arcades?