Best foot forward, Geralt.
You know what's out? Binary morality in RPGs. You know what's in? Vast and complex constellations of individual "reputations" that measure how each particular faction, town, and individual you come across feel about you. It worked in Fallout: New Vegas and, by god, it'll work in anything else you're tempted to stick a light side/dark side meter into.
And you know what? It'll work in The Witcher 3, too. Or it will if a modder named FreakVip has anything to say about it. They've created a mod called, prosaically, Reputation System (via IGN), which promises to change the game in such a way that "Geralt's choices and behaviors" will impact a new system of reputation points, which will in turn influence "all kinds of activities" for the White Wolf.
The mod adds a reputation level for Geralt across five areas: Temeria (White Orchard and Velen), Nilfgaard (Wizima and the army camp), Redania (Novigrad, Oxenfurt, and regions across the Pontar River), Skellige, and Toussaint (from the Blood & Wine DLC). It goes from "Hated" all the way to "Respectable," with lower levels making life predictably more difficult for our witcher hero.
How much more difficult? Well, without being able to get the Witcher 3's voice actors back in a booth to record new, reputation-specific dialogue, it's mostly restricted to matters financial. If an area hates you, you'll have to pay 30% extra for goods, accept 70% less when selling, deal with harder bargaining, and worse gambling odds. Being respected, meanwhile, flips all that on its head: Goods are cheaper, people will buy your stuff for more, and so on.
How you gain or lose rep is pretty self-explanatory. Anything that annoys an area's guards—getting lairy or stealing—is liable to ding your points. Meanwhile, solving quests in a way favourable to a region's inhabitants will, naturally, make them more amenable to you, as will completing monster contracts or winning horse/boat races and fist fights, which is also how it works in real life.
It's a clever, and fairly simple, way to add a bit more reactivity to The Witcher 3's world, and it's compatible with its latest patch version (4.04). If you want to check it out, just download it from Nexus Mods and shift it over to your main game folder. Then be on your best behaviour.
