I'd describe it as a steampunk crime caper, in which Inspector Noridel and the faithful Sergeant Crayford are set on the trail of a killer who tears the hearts from his victims. When an aristocrat is slain in such a way, things escalate and Noridel is fighting to keep his job amid scrutiny from those higher up the chain of command. Witnesses describe the killer as being an angel, so what exactly is Noridel chasing? It's not a complicated plot, but it's a compelling one, and that alone keeps you reading.
Some steampunk stories can sometimes feel like the steampunk elements have simply been 'bolted on' to satisfy a list of criteria (Cogs and brass? Check. Steam? Check. Automata? Check. Airships? Check.) but in The Angel of Shadwell, the elements are so integral to the plot that the story wouldn't work without them. Beyond that, Templar uses them in a wildly inventive way, and his cast of miscreants reminded me of the more restrained outpourings of China Mieville. Noridel and Crayford are both likeable protagonists, while the uneasy truce between Clock and Flesh (i.e. automatons and people) seems rife with possibilities that I hope Templar explores in the future.
All in all, it's a quick read, and highly enjoyable. Five blunt pencils out of five!