Sin delves deeper into the world of Spire, and includes:
• Two new classes: the divine confidence trickster Gutter Cleric and the necromantic bureaucrat Mortician Executioner • Extensive sections on the Crime, Order and Religion domains with dozens of new abilities, hundreds of plot hooks and fiction tidbits, four evocative maps, and dozens of beautiful illustrations by Adrian Stone • Three ready-to-run scenarios, pitching the player characters headlong into a world of squabbling holy orders, mysterious librarians, demonic artefacts, overclocked noir magic, interdimensional breaches and hotwired harvest god avatars
A really great supplement, with a great roundup of religions, law, and criminal organizations in the city of spire, several very fun-looking adventures, and lots of the typical Spire weirdnesses. I particularly loved the 'extremely assassinatable' npcs presented throughout -- I know this is part of the kickstarter rewards, but it was so wonderfully created, every one of them is a story hook in and of itself.
If it's missing anything, it's just that I wish we knew more about some of the cults indicated on the map as icons (Great glass eye etc) because I'm so curious about some of the cults big enough to get marked down -- though I know some of these were originally added and had to get cut for space (the golden serpent is its own supplement now) so it's understandable that we don't have them here.