James Sutter, fiction editor (and author) over at Paizo, made a compelling case in a Q&A session about the value of the "Hollywood pitch" for new works. Something succinct, quick and dirty, not very detailed, but which gives you an idea very quickly about what to expect. This is often done in such a way that it combines two or more successful, well-known titles, memes, or characters to give a cognitive shorthand to what kind of feel you can expect.
So, for example, Dave Gross's first two major Pathfinder stories are described, in Hollywood pitch style, as "Half-elf Sherlock Holmes and tiefling Watson" and "Indiana Jones meets Brotherhood of the Wolf in Transylvania" respectively. Does that really completely sum up either work? Well, no, of course not. But it does a good enough job, and it's extremely fast, and it's evocative and compelling. Who wouldn't be interested in seeing those particular combinations? Well, no doubt several people, but not people who are likely to read this blog.
DARK•HERITAGE's Hollywood pitch goes something like this: "The Black Company and The Godfather meet spaghetti westerns and Pirates of the Caribbean." If the initial pitch sounds intriguing enough, and the Hollywood agent says, "let's do lunch and you can tell me more about this project," then I can start getting a bit more into the details.
DARK•HERITAGE is firmly rooted in the fantasy genre, and has some of the typical fantasy conventions you'd expect, especially if you're a fan of either old school Sword & Sorcery or this newer type of dark fantasy featuring criminals and anti-heroes as protagonists. But it also has a strong vibe of supernatural horror and Yog-Sothothery--magic exists, of course, but it's never a good thing, and kindly or wise wizards are replaced with terrifying and post-human (or human, but who aspire to transcend that state) sorcerers which are thankfully quite rare. Rather than save the world quests to stop the machinations of dark lords, or restore glorious kingdoms, DARK•HERITAGE is often about the skulduggery and intrigue of amoral movers and shakers--corrupt rulers, powerful sorcerers who pull the strings from behind the scenes, organized crime, and nihilistic cultists. Or, more accurately, it's about how Joe Blow fantasy characters (player characters, or story protagonists, either one) get caught up in that skulduggery and intrigue, and find their lives buffeted by forces beyond their control, and their attempts to take the reins and successfully navigate through them with their lives and sanity intact. Their motives are rarely altruistic or heroic and their personalities are often cynical, pragmatic or even world-weary. They're like noir characters who find themselves in a dark fantasy-horror hybrid setting.
The setting is fairly wild--part Arabian Nights, part Spanish Main, part Crown of Aragon, part Old West, part Lovecraft, part Clan of the Cave Bear. But most DARK•HERITAGE adventures will take place in one of three places: out in the wild, that's like Cowboys & Indians type settings except with much more dangerous wildlife all over the place, or the high seas, with Barbary and Spanish Main type pirates, or deep in Spanish or Italian style picaresque cities with thieves guilds, assassins, spies and cultists roaming the streets after dark.
The D&D elements are fairly muted; magic is house-ruled to act more like Call of Cthulhu style magic, characters don't become powerful, god-like superheroes, or adventure for XP and profit, and the palette of character options (especially races) is a more sword & sorcery like human and mostly human yet exotic "touched by dark magic of some kind or another" variants; there's no lordly elves, dour dwarves or cozy hobbits here. Villains are like more dangerous versions of the main characters--there's no conveniently cartoon-like always evil races; no orcs, goblins or whatever. No dark lords in the traditional sense.
While from a rules perspective, I've toyed with many options, including various house-rules for D&D 3.5, Pathfinder, or even Old School Hack, my preferred and recommended ruleset is d20 Past, a sourcebook for the d20 Modern roleplaying game. With a few houserules to introduce my custom elements, it's good to go without much modification.
While that document appears to be intimidatingly large, in reality, it's just clarifying, and giving full text houserules for things like the specific races, languages, etc. of the setting, as well as repeating (with some minor modifications) the entire rules for familiars and a few other things. In reality, the rules changes to d20 Past are quite modest.