Anyone interested in game design should read the Anatomy of a Game series that Jeremy Parish has been doing: http://www.gamespite.net/category/games/anatomy-of-a-game-ga...

Right now he's doing Final Fantasy 6, but has previously done Super Mario Bros., Mega Man, Castlevania, Castlevania II, Castlevania III, The Legend of Zelda, The Legend of Zelda II and Metroid. Unfortunately, I can't find a good synopsis page which links to the games individually.

edit: synopsis page here, but Jeremy recently moved all of his content back onto his blog, so this doesn't contain his recent stuff on FF6: http://www.anatomyofgames.com/anatomy-of-a-game/