Back when everyone else had a computer we had an Atari. The one game that could keep you trapped for hours in front of this console was Centipede.
You are in the mushroom patch (I don't know why it was mushrooms) and a Centipede is coming down to get you, very much in the style of Space Invaders, but with all sorts of obstacles in the way.
I remember spiders particularly as they used to drop straight down the screen, and fleas, I think, used to jump across it. So all you had to do was shoot the chunks of the centipede (and if you shot him in half there would be two of them) until he was completely gone, whilst avoiding all the other creepy crawlies.
The centipede just kept getting faster as you progressed through the levels. Used to keep my mum amused for hours!