Gamasutra has yet another interesting installment of their "game design essentials" series up - this one on game mechanics shrouded in a cloak of mystery. Everything from Bubble Bobble to Street Fighter makes the list, with explanations of why the game made the (not ranked in any particular order) list and what it says about game design more broadly. Why does this stuff matter, anyways?
The existence of so many things hidden in the game that don't have to be found lends the game a certain quality, one best described as verisimilitude. Verisimilitude is a useful word to use in describing video games .... Properly used, the word means that there seems like there is a world outside the borders of the screen, happening regardless of what the player does. It implies the existence of a fully-fleshed world, one that's more than a mere collection of polygons or tiles that might as well be sealed in Plexiglas. It allows a game to better enable the player to forget that it is, really, just a game.
An interesting trip down memory lane and has some interesting connections to current and future game design.
Game Design Essentials: 20 Mysterious Games [Gamasutra]