A mildly less sleep-deprived and hopefully shorter return to the theme of rulebook content.
Specifically, I'll try to actually answer Shannon's question instead of rambling incoherently about other stuff.
So, what is useful in presenting a setting? I freely admit I'm not the best person to answer this because I've mostly played RPGs whose content I was already familiar with, from generic fantasy D&D to the metal insanity of Warhammer 40,000. But I'll give it a go.
One thing that I think is important, but not easy or straightforward to convey, is the general mood of the setting and its inhabitants. Although some settings may be played in multiple tones, in general they seem to lean towards particular tones because tone is partly a feature of setting mood and setting features.
For example, a setting based on early 20th century science fiction will tend to have an optimistic mood. Humanity is generally in a state of steady progress, even if they're at war. Problems are generally solvable. Enemies are fearsome, but will be overcome; often enemies aren't the traditional kind, but mistakes, problems or forces of nature that Science or Guts or Humanity will cope with. The population might be pessimistic about some major problem, but are usually not downtrodden, treacherous (on a species scale), every-man-for-himself or nihilistic.
In contrast, the default setting for 4E D&D is what you might call embattled heroism. The setting is explicitly "points of light in a dark world". Civilisations have come and crumbled. Savage monsters, bizarre magic and murderous evil creatures run rampant, while from the ranks of the remaining civilised races come not pioneering scientists and Aces of the Interstellar Guard, but thieves' guilds, sinister cults, self-interested nobles and other villains. While larger settlements and kingdoms might seem content, everyone is aware that invasion, monsters or disasters are always lurking on the horizon. Even the civilised kingdoms tend to feature deeply unequal societies, inter-species tensions and miscellaneous injustices. Powerful wizards stand coldly observing as orcs demolish the nearby town, unwilling to intervene. All too often, villages call in heroes for aid, only to demand payment for equipment vital to said salvation.
Mood can also include a general sense of things like how people feel about the government, how stringent laws are and how law-abinding people are, and how large-minded NPCs will be about unusual and unreasonable behaviour from the PCs. In Shannon's example, it's a wartime setting, and these can go either way. In some cases, extraordinary behaviour is expected because there's a war on. In other cases (such as when invasion is imminent) the populace are constantly suspicious of any departure from the norm, and the uniformed services are on the case like a shot if anything's reported. This kind of information can help illustrate the expected approaches, attitudes and behaviours of the PCs.
Another useful thing is to outline the general hustle and bustle that surrounds the PCs. It's hard to demonstrate what's interesting and relevant if the players and GM aren't sure what's normal. This can vary from showing how NPCs tend to spend their time (which may also be what PCs do in downtime), to setting the boundaries of "ordinary". If an orc walks into your bar, is that utterly trivial (city full of orcs), mildly unusual (numerous friendly orcs), noteworthy (orcs are rare or hostile), unheard-of (orcs are hated or banned) or cause for panic (orcs are exclusively seen in rampaging hordes)? If something magical occurs, a rift in space-time opens or the ship receives a distress call, are those strange and noteworthy events, or par for the course?
Similarly, some general information on the type of economy and occupations common to the setting can be enlightening. Is it largely a subsistence economy, mercantile, capitalist? Do people tend to choose their occupations, or are they constrained by heredity, feudalism, government diktats, an all-seeing Computer or the visions of oracles? Even in a modern-day setting, specific regions and cities vary considerably in the major industries and occupations, and these have significant influences on everyday life. You can infer an awful lot from knowing that Townsville is a large dormitory town, Smogburg is a declining industrial city, Twaddlehampton is a village full of authors who fled the city and retired senior managers, and Mucking is a rural hamlet where people actually work on farms.
In fact, let me draw some inferences to demonstrate.
- Townsville probably has few local amenities. Everyone shops at the out-of-town supermarkets on the way home, drives the kids to school and either watches the telly at home or goes to the city of an evening. There'll be some takeaways, and bored teenagers kicking walls. Clubs, churches and libraries will be small and mostly empty; nobody feels part of a community. Most are probably here "temporarily", even if they have been for several decades. The people work in white-collar jobs, but not very well-paid ones. There are few buses, and they take long, inconvenient routes. Most people don't know their neighbours, let alone any local gossip, and they keep to themselves unless something really dramatic happens.
- Smogburg is mostly poor. There's heavy unemployment, decrepid buildings and a notable crime rate. Fine old buildings, built in the flush of the industrial revolution, are often boarded up or fire-damaged. Sixties concrete monstrosities are everywhere, held together by the fly-posters of decades. Cheap alchohol shops, takeaways, pound shops, charity shops and moneylenders are frequent; there is probably Marks and Spencer, but no Waitrose for miles. Despite this, community groups are stronger than in Townsville, as people feel part of something. The streets feature charity collectors, Big Issue sellers and evangelical preachers. Fat tower blocks loom sullenly over the horizon, some of them brightly coloured from recent renovations that seemed cheaper than knocking them down. There are interesting shops here, but not the quirky hipster kind; Smogburg is cheap enough that almost anything can stay open somewhere, often in a single room over a charity shop, even when they only make one sale a week. You can buy almost anything useful here, if you can only find it. People are often willing to talk, particularly in the town centre; some of the estates and tower blocks are a different matter unless they know you. Generally, neighbours know one another, even if they don't like each other, and plenty of people were born and bred here.
- Twaddlehampton has a number of thatched cottages, some of which weren't even originally thatched. Most of the houses have gardens, which are lovingly tended. There are wide pavements, and people stop to talk in the streets; few of them have lived here more than a decade. Life has a slow pace. People pride themselves on their community spirit; life is full of village halls, tea dances, policemen's balls, Scouts and Guides, National Trusts, the more traditional-sounding kind of churches (whose rather good associated schools are a non-negligible cause of their large congregations) and Best Kept Gardens. Everyone either prides themselves on not owning a car, drives something old and cinematic, or has a massive 4x4. Nobody wears tracksuits unless they're jogging. There are numerous village shops with tradition names like Jones and Son, several cafés, and pubs that serve both Yorkshire puddings and something with chorizo and jus. People are Pillars of the Community, but also gossip ferociously and harbour deep grievances. The surrounding region is rural, but in a mildly scenic way, and the roads are well-maintained and offer surprisingly quick access to the nearest city. There are no major roads through the village, and no wind farms nearby. Strangers will struggle to get plot-relevant information unless they seem like they "fit in".
- Mucking has houses that are generally in pretty good nick, but have clearly been patched and cobbled together repeatedly. Old extensions show where tiny farm cottages have turned into houses more or less acceptable for the modern era, with lots of outbuildings in strange places, now serving unexpected turns as motorbike storage or generator room. There might, possibly, be a post office. A major road runs at least nearby, and likely through the middle of the hamlet; it probably seemed like a good idea in the age of the mailcoach, but now it's almost impossible to get your car out of the garage, even with the mirrors stuck all over the place to spot oncoming vehicles. Everybody drives a 4x4, because the roads have a 45-degree incline and it snows a lot here. When the rains come, they paddle instead. A tiny village shop offers newspapers, a number of mundane items, and five or six really odd things for reasons you can't imagine; it's open sporadically and unpredictably. People will either talk to you for several hours without drawing breath, or clam up instantly when they hear a "foreign" accent. Intimate knowledge of their neighbours and local area is almost inevitable. Travelling around the region is nigh-impossible unless you have good maps or local knowledge; the roads are tiny, winding and occasionally terminate in the middle of a field.
- If something weird happened in a house last night, the people of Townsville won't know anything about it. Smogburg will have noticed something, and word will have gone around, but they might not want to discuss it with you (especially if you look like trouble). Mucking will probably know something but won't like to gossip unless they dislike that neighbour. Twaddlehampton will act like they don't want to gossip, but need very little prodding.
- You can believably pick up an occult book in both Smogburg (in a market or from a shoplet over a chippy) or Twaddlehampton (in a rather nice second-hand bookshop or church fair), but certainly not in Townsville. Mucking might have some, but not in the shops; they'll be old family things.
- The police will turn out quickly in Smogburg (because real trouble happens there) and Twaddlehampton (because the middle-class residents are very vocal), but are much less responsive in Townsville and Mucking where urgent problems are rare. Police visiting Twaddlehampton tend to be polite, appear to take things seriously, and don't; police visiting Smogburg are cautious, somewhat jaded and suspicious of accounts. In Townsville they are pretty matter-of-fact about the graffiti and stolen cars.
- The average minister in Smogburg is likely to be from a humble background, evangelical and has a good chance of being from an ethnic minority; they have a very good idea about the sad and seedy sides of life. Twaddlehampton has an Anglican vicar, of course, who went to Cambridge and is very good at the theological side. Mucking's little parish church features an ex-farmer with excellent knowledge of working life and a pragmatic outlook, who can help birth a cow, get a tractor out of a ditch, and has attended a fair number of nasty accidents. If Townsville still has a minister at all, they are probably Methodist, fairly cheerful, very ordinary, work part-time as a nurse as well as running three local churches
How educated (and/or misinformed) do people tend to be about the world, other people, science and magic? This will inform their opinions, their reactions to events and their openness to new ideas. Is this a setting where knowledge is free, a melting-pot of ideas, an ignorant hotbed of superstition, a jingoistic and xenophobic world, or under the sway of a despotic government that imposes ideas it finds convenient?
Other features of daily life might be the species and cultural make-up of a setting, the technological and magical prowess of the major civilisations, and where life falls on the scale from Galactic Harmony to There Is Only War.
Now that we know something about the ordinary, what is extraordinary? These (in most games) will indicate the sorts of things the PCs get involved in. It can be a mixture of "things that are unique about this setting" and "things that are particularly important in this setting". PC-centric features may be long-standing problems, interesting places, organisations, events and so on. Predatory monsters are one example; powerful psionic guilds are another. An array of unexplored worlds in a sci-fi setting indicates that PCs might usefully spend time exploring them; a network of monuments left by a vanished race tends to suggest that more on this topic can emerge. If bandits are constantly holed up around the countryside attacking merchants, PCs may be called on to act as guards or bounty hunters, whereas if supernatural beings are rumoured to turn up occasionally but not officially acknowledged to exist, it's more likely PCs are going to encounter them through accident or investigation. As such, to some extent the nature of these features will depend on the game genre, particularly in terms of how well-known the unusual features are.
D&D frequently features predatory monsters that need stopping, ancient ruins that need exploring, and unknown parts that need knowing. Deathwatch, by its nature, highlights alien incursions that must be stopped, but there are also wrecks to scour, monuments to investigate, heretics to hunt down and powerful Imperial emissaries to negotiate with. Traveller features anything from alien ruins to drifting spaceships, astronomical anomalies to trade disputes, but the Corporations are a relatively mundane feature that is nevertheless very prominent in shaping PC activities. Ravenloft's most notable features are the array of sinister rulers who empathically shape both their domains and their subjects, and the constant threat of the undead.
As best I can describe it, you're looking at the kind of things that players and PCs alike are expected to take notice of. These are departures from everyday life, and things that make the PCs want (or have) to do something, whether that's grab a blaster, hit the library or start planning a road trip. In some games, these overlap with hooks, although they may not be designed to introduce specific adventures in the way hooks are. In other games (investigative games may be a good example) these will tend to turn up sometime after the initial hook; the "letter from an old friend" draws you in, but the antediluvian artefacts and the dreams they're provoking are the meat of the scenario.
These are also likely to be the features that help to sell a setting. Where the daily grind details establish the broad sweep of the setting, it's the cool details that really bring it to life and inspire the GM with ideas. This is the sort of thing that has you imagining how you, personally, could use it.
...I don't feel like I'm explaining this very well, but I tried.
Settings may be very focused or patchwork as anything, but either can be made to work. One of the important things here is establishing coherence. What I mean by that is giving a sense of how these things fit together in a single setting, both in a broad sense, and in a practical sense for the GM. The real world, for example, has wildly varying levels of technological sophistication in different places, even within the same country. In a game, though, where it's harder to convey the nuances and gradual shifts that create those real-life situations, disparities can seem unconvincing. Our recent Numenera game took place over a small area that encompassed a wilderness, a forest town besieged by animals, a spa town (which in my head is all Georgian, although I suspect Monte Cook has never been to Bath or Harrogate) and what felt like a Midwest frontier town. Especially for a first game, this didn't feel particularly coherent to me.
I can't really offer any specific advice here, because every instance has different features to integrate. Deathwatch mashes up astonishing feats of heroism, a brutal and oppressive culture, high technology and astonishing ignorance, in a way that allows for everything from primitive jungle planets to towering hive-cities, and lets PCs and NPCs alike pull off technological tricks while remaining suspicious and wilfully ignorant of unknown machinery. The setting allows for mysteries, brutal combats, oppression, NPCs interfering in the PCs' lives and missions, PCs exerting authority on those below them, paranoia, blind faith in authority figures and a range of moral approaches from stark black-and-white to flat grey.
If there are a lot of "yes, but why..." questions to be asked about the setting, substantial discrepancies, or dramatic gradients of some feature or other, then these either want to be sources of plot and interest for the characters (good in games where PCs don't understand much in-character, and where the world is odd) or need explaining.
I think to some extent it doesn't matter how cool the individual features of a setting are, if the GM (and thus the players) can't establish a coherent vision of the setting, they will struggle to run satisfactory games in it. It's like the difference between a vignette and a story. You can't improvise around a framework that isn't there; a pile of individual scaffolding bars isn't enough, no matter how shiny each one is. It's important to be able to make predictions, draw inferences, and otherwise play around the things that are made explicit, without finding yourself at a loss or contradicting important aspects of the setting.