Sins is a sleek, post-apocalyptic supernatural rpg with a focus on storytelling.
And if you're familiar with New World Of Darkness, Sins is going to be very easy to learn as a lot of it feels close to the structure, layout, design, tone, and mechanics of the NWoD splats.
Sins' PDF is 360 pages, with spectacular graphic design and beautiful art, and its gameplay sits in that same "medium crunch" area as NWoD's.
Content-wise, Sins is the intersection between Walking Dead, Gears Of War, Stand Still Stay Silent, Cthulhutech, and Fallout. There are supernatural powers, strange phenomena, corpse armies, derelict ruins, and civilization working to pick itself back up off of the mat. There's a mature angle to everything, but it's not hyperbolically mature.
Sins' mechanics are d6 pool based, with target numbers and number of successes mattering. Your pool on a roll is your relevant attribute + fate (i.e. your level) against a target number of 7 - your relevant Skill, and you're hoping to reach a number of successes determined by the GM based on the difficulty of the task. There's a meta-currency called Focus which you can use to affect rolls, and which you can recover with cool narration. Also there's health levels which are structured into different categories, and a variety of unique supernatural abilities to choose from.
Combat has a fair bit of complexity, but Sins is still on the storygame side of the storygame/wargame divide. 'Tactical storygame' is probably a good descriptor. There's universal combat maneuvers, cover, weapons with stats, and a lot of attention has been put into making the players' combat options varied, but you're not required to break out a battlemat.
Lore-wise, there's a few places where the book explains a thing in a way that is less helpful than if it hadn't explained it at all. For example, some of the setting's human settlements practice slavery. The book's explanation is roughly "everyone knows it's wrong, but there's a need for disposable manual labor" and "it's better than killing the population of the settlement you just conquered." This feels like a *really* optimistic take to me, although your mileage may vary.
I also got a bit of dissonance from the "What Remains" section of the book, which goes over various areas of the world and how they've been affected. Western Europe and the United States and Canada feel pretty solid. The Middle East and Asia do not. To me at least, they feel like weird caricatures, especially in contrast to the way western Europe and the upper half of North America is described.
I don't get the impression this was meant to be malicious---on the contrary, safety mechanics are provided and there's warnings up front about the book's tone and that it discusses slavery in its setting.
But I don't think a second draft of the Middle East and Asia sections would hurt. Nor would cutting them.
Overall, I think this last detail makes for an achilles heel on an otherwise engaging engine and setting. Without it, there'd be no caveats on my recommendation. With it, I don't really have a good guess for how each individual person is going to react to the game, and I can't just broadly recommend it to everyone who likes NWoD and post-apocalypticism.
I have no idea if a patch here would be a logistics nightmare, or would destabilize material that's been written in other products, or would contravene anybody's creative vision, but I'm happy to change my review if things get changed.
Honestly if it turns out I'm just straight wrong in my reading of the What Remains section---which I'm not gonna rule out---I'm happy to change it too.