Hitman is methodical and systems driven, but otherwise doesn't have much in common with 'immersive sims'. I've only played Blood Money (great) and Absolution (shit), but I couldn't actually tell you much about the story, besides that it is not to be taken seriously. Writing wise, everything is in aid of your mission. No world-building that I can remember, just giving you hints and reasons to feel good about killing your targets, who are all monstrous people.