I love having any excuse to share this link.
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the big question of level design - and i mean that every level design lesson i ever write will be a response to this question - is: how do i teach the player these rules? an unfortunate trend in contemporary games is to spell out every detail in a hand-holding “tutorial” session at the outset of a game - unfortunate because it shows both a great deal of contempt for the player’s intuition and a lack of confidence in the designer’s own design. but more than that, it’s a design failure because it tells the player the rules instead of allowing her to learn them.
what if the first level of the game were laid out in such a way that the player could learn the rules simply by playing through it, without needing to be told them outright?
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The article's a critique of World 1-1 being the perfect tutorial level for Super Mario Bros. Go read it.