I've previously expressed the opinion that content coherence helps a game feel memorable (in a good way!). Today I'd like to describe this idea in a little more detail.
By "content coherence," I mean the principle that every piece of content in the game -- every object, every mechanic, every interface component, every visual and every sound and every word -- is consciously selected and built to echo every other piece. The attributes of each element should be similar in some way to the attributes of all other elements.
(By extension, this also means that any element that does not contribute to the fundamental vision for the game must be cut with complete ruthlessness. As with novelists, the worst sin a game designer can commit -- other than to make boring art -- is to fall in love with some piece of a game that doesn't directly advance the vision for that game.)
This means being aware not only of the overt appearances of content elements but also of the deeper connotations of individual elements and the functional properties of linked elements. By understanding the attributes of content elements, designers can choose elements with similar attributes. And by choosing elements whose attributes are typically associated with one or two particular feelings or ideas, all the individual pieces of game content will echo and reinforce each other to form a particular and uniquely distinctive whole product.
Without this effort, players will experience the pieces of a game as individual components. The "good" parts will stand out, but so will the "bad" parts. Players are likely to remember the game -- and describe it to others -- as a loose collection of individual mechanics, rather than as a single recognizable experience. This can also happen when elements chosen for the way their attributes are perceived in one culture mean something different in another culture. In this case (as in games made for the Asian market when played by Western gamers and vice versa), all the internal attributes may cohere, but the overall effect is less than desired because some of the attributes of various game elements aren't interpreted as expected.
That said, paying attention to content coherence makes it easier for players to perceive a game as a unified whole. Even weaker elements will be better tolerated as long as they are perceived as contributing something to the overall feel of the game. This not only makes the game more satisfying to each player, it pays off in helping players sell the game to other gamers because it allows them to explain the fun of the game as a simple concept -- one short sentence to say what the whole game is "about."
Minecraft is a beautiful example of this conceptual clarity. What's Minecraft about? It's about mining (breaking blocks) and crafting (putting blocks together). The survival aspect adds excitement to the core Minecraft experience, but ultimately Minecraft is easily understood and described as exploring a world by reducing it to components and putting those components together in new ways. You mine, and you craft.
Every part of Minecraft supports (more pointedly, every part of Minecraft is consciously chosen to support) every other part, creating a very high level of content consistency. Not only can the terrain be mined, so can everything else -- trees, animals, monsters, even water and lava can all be "mined" for resources which can then be crafted into new objects. Every piece of game content is a careful extension of this simple basic concept, and Minecraft becomes easy to play and easy to recommend as a result. A similar approach was applied in Portal, in which the interplay between the indirect portal mechanic and the misdirection of GLaDOS was so strongly defined that players imagined resonances beyond those overtly designed into the game.
But there's perhaps an even better example of remarkable attention to thematic detail at the design level, and I can give it to you in three words: FUS ROH DAH!
The Elder Scrolls series (at least the core games) has always been a good example of content consistency. Through each game, the world of the Elder Scrolls is carefully constructed from individual pieces of content that support each other and combine to form a recognizable secondary reality of art, sound, lore, and play mechanics. Designer Ken Rolston recognized that an important narrative aspect of many RPG worlds, with which he infused the Elder Scrolls games, is what might be called "the melancholy of lost civilizations." This concept, mentioned near the end of the Gamasutra article "Rolston: Physical And Virtual Artifacts Crucial To Narrative Designer's Job", appears to have become an important tool in designing the more ambitious later Elder Scrolls games. Most of the elements in modern Elder Scrolls games are related in some way, either directly or subtly, to long-forgotten histories of beings and cultures that once strode the world. This concept helps to guide the selection of content, from stories of the lost Dwemer and debased Falmer to their artifacts, from the weathering of broken towers to the ambient music of exploration.
Skyrim does a visibly good job of this, but it was true to a fair extent for Oblivion as well. Some gamers criticized Oblivion as a "generic fantasy world." This criticism is leveled almost exclusively by players of Morrowind, the previous game in the Elder Scrolls series. Morrowind featured unusually imaginative world elements that evoked the strange "dark elf" geography and culture. Oblivion, as an expression of the Romanesque geography and culture of Imperial Cyrodiil, was necessarily less wild, but it still effectively communicated the distinctive Elder Scrolls feel through its components. The lore found in books and the dialogue of NPCs (which strongly renders the races and their distinctive cultures and game-mechanic strengths); the way arms/armor, magic, and sneaking work; the artwork and audio through which all these elements are expressed, including tumbledown Ayeliid ruins -- Oblivion tied all these things together effectively. Even stitching the overworld into an apparently seamless whole (preserving this effect from the prior PC-based games) supported the feeling of world-consistency in Oblivion.
Skyrim, however, refines this internal coherence to a remarkable level. The visuals and sounds of the chilly land of the Nords (the next of the races from the Elder Scrolls universe to get their own game after the Imperials, the Dunmer and the Bretons/Redguard) are specifically crafted to be consistent with the Elder Scrolls lore of lost civilizations and to support and highlight the spell/sword/sneak triad of mechanics for exploring (and surviving) the remains of the past. The new feature of Skyrim -- dragon "shouts," which are up to three words in the language of dragons that produce some useful effect -- also fits into and extends the existing lore/world/mechanics components of Elder Scrolls games, as does the return of the dragons themselves.
To understand just how far Bethesda has taken the concept of content consistency, first listen to the opening measures of the main theme for The Elder Scrolls II: Daggerfall. Next, listen to the main theme for Morrowind by composer Jeremy Soule. (You could also hear essentially the same theme reworked for Oblivion, starting in particular about 17 seconds in.) Now listen to the first measures of the theme for Skyrim, especially at about 58 seconds in. You'll notice that all of these overtures emphasize a sequence of three notes. The Morrowind/Oblivion and Skyrim themes in particular share a very similar rhythmic structure: 1-2-3, 1-2-3, 1-2-3, 1-2-3. On its face this is a nice callback to Morrowind/Oblivion by Skyrim, but there's more to it.
The lore of an Elder Scrolls game is important not only for the "lost civilizations" motif but because it supports and reinforces the gameplay, which as noted is the triad of magic, melee and stealth. (Trine is another game that uses this model, and of course there are others as well -- it's a good system.) But the 1-2-3 beats of the main musical themes in the two most recent Elder Scrolls games also echo this triad. With every dah-dah-dah, dah-dah-dah, the player is reminded that there are three forces at work in the world.
That may sound like too much of a stretch, but consider Skyrim's dragon fights. If you've got the music turned up when one of these ancient creatures attacks, you not only hear the three syllables of "Dovahkiin" (i.e., "dragonborn" -- also three syllables) being sung, which is the part of the main theme at about 00:58, the music precedes this with a repetition of three manly grunts: 1, 2, 3... 1, 2, 3. And the second chorus of "Dovahkiin" actually plays the 1-2-3, 1-2-3 Morrowind/Oblivion theme in the background.
That's where the dragon shouts come in. When your character shouts "FUS ROH DAH!" you the player are adding your own three-part expression to the gameworld. In the course of playing the game you collect each of the three words of the iconic FUS ROH DAH shout. Having three words in a shout echoes the three styles of action in the game. And unleashing the full three words of a shout is echoed by the three beats in the heroic music that plays when you fight a dragon for your life. I can't think of another game that has achieved this level of thematic consistency in its form and content.
Bethesda may have gone even deeper than this. In the world of the Elder Scrolls, there are three racial archetypes (elven, human, beastfolk); in Cyrodiil's pantheon of mortal divinities there are the "Nine Divines" (three groups of three); Tamriel has nine provinces; and Skyrim has nine "holds." It's possible that these are coincidences -- this kind of numerological pattern-finding can be taken too far. But it's also possible that these aren't accidents, or perhaps have been retconned from arbitrary creations into additional Elder Scrolls-specific support systems for the "three ways to play" model.
Even if not every one of these is a deliberate design choice, there's still plenty of evidence that Bethesda has consciously tried to organize each Elder Scrolls game with ever more attention to internal consistency. In general, by thoughtfully choosing and implementing features so that every element reinforces every other element, and by insuring that every element supports the intended play experience, gamers can quickly understand and easily describe to each other the specific deeply satisfying entertainment that such a game delivers.
Of course not every game is going to need a fanatical degree of integration among its elements. A match-three game or kart racer can safely ignore a lot of the effort required to build an internally coherent world.
Even so, it helps to make sure that anything that does go into a game is chosen to work well with everything else, and that all selected elements help to express the game's core concept as powerfully as possible. Skyrim's designers may have used "unrelenting force" to achieve this effect, and Portal and Minecraft may have iterated to a remarkable degree on the yin and yang of their core mechanics, but every game can benefit from content coherence.