"Black Hole" was the first machine to feature a lower playfield viewed through a window in the upper playfield.It was touted as the highest-grossing pinball game of all time shortly after its release, partly due to (or despite) the fact that it was the first pinball game which cost 50¢ to play (although many argue that Williams "Black Knight", and "Firepower" were already at 50¢ before the release of Black Hole).