Space Invaders made such a significant impact on the videogame world that for a long time after its release, the only reasonable way forward for game designers was to create weird and wonderful variations on the theme. Centipede is a prime example of how the concept could be modified to produce unique and popular titles that still fed the voracious public hunger for single screen shoot-'em-ups.
Playing Centipede is relatively easy - after all, shooting everything that moves takes little in the way of strategic imagination. But explaining the rules, purpose and gameplay is another matter entirely. Although it doesn't detract from the high speed, exciting, hyper-twitch gameplay, no matter how many virtual coins I pour into Centipede I still can't quite fathom what the hell I'm actually supposed to be doing.
My ship thing (unverified sources tell me it's a "gnome") has a limited range of free movement around the bottom quarter of the play area. This play area (I'm gonna go out on a limb and say it's a garden) is rife with mushrooms which react in a similar way to the bases in Space Invaders. Enter the game's namesake, which snakes its way down the screen to assail our misshapen gnome. As it hits a mushroom, it about turns and increases it's decent all the more rapidly.
All manner of other creepy crawlies zoom about the screen, adding more fungi, altering the 'shrooms to change the action of the Centipede and generally finding new and inventive ways to end your life. In all honesty, it beggars reason to try and fathom what the hell's going on in Centipede, and trying to do so only serves to ruin much of the game's enjoyment.
Shoot stuff, stay alive, and keep adding credits. That's what Centipede's all about, baby.