Centipede
1980
Designed by Ed Logg and Dona Bailey.

One of the most interesting things about these games is how abstract they are. Centipedes don't move like this in real life -- going back and forth until they hit mushrooms and drop down a level. In fact, nothing in this game matches its real-life counterpart very well. The game is composed entirely of invented mechanics. This is nothing special in the field of puzzle games, but in a action game, it's novel.

But then, for what is basically a shooter, there's a great amount of strategy to Centipede. The most inert things in it, the mushrooms, turn out to be the key to success. If there weren't mushrooms it'd be easy to clear board after board. It takes time to chip away at them, shooting centipedes creates more, and if there are too few on the screen the game drops in mushroom-producing Fleas.

Meanwhile, mushrooms hasten the centipede's descent, they block shots, they give scorpions something to poison which can make the 'pede much more dangerous, and they even block movement if they're low enough. All four of the game's enemies affect, or are affected by, mushrooms in some way.

Centipede's difficulty curve is also a bit special, for there are actually two curves here added together. The game gets harder by level, in that every time the player clears a centipede the next one is slightly harder, with a faster 'pede and more initial heads, and it gets harder by score, which affects overall game speed and enemy behavior.

This helps to mix things up a bit, and also makes the game less vulnerable to hunting strategies that freeze the level progress but increase score. Although the game still has those...

The distinctive winding motion of the centipede makes possible an amazing exploit. An old issue of Joystik illustrated the technique, attributed to one-time Centipede champ Eric Ginner, demonstrating that by leaving three mushrooms on one side of the screen, both the centipede and any extra nuisance heads will be trapped between them and the side in a constantly-winding blob, leaving the player entirely safe.

Due to the game's per-level difficulty advancement, if this is done on a "full centipede" board, one that starts with no individual heads, then the game will never drop in fleas to bomb the player or add mushrooms, meaning the only things that can hurt the player are the spiders that show up periodically. By just hunting them the player can accumulate high scores with minimal risk, although it's kind of boring to play that way.