Stolen Souls picks up the metaplot threads from 4th-edition's Storm Front and brings them into the current 5th edition. Once again, there is something weird and creepy happening in the Sixth World (a nanite-carried virus that overrides your personality), which might be bad news for your Shadowrunner down the road, but will certainly offer ample opportunity for profit in the meantime. This book is mostly fluff, but in my opinion it's the fluff that makes the Shadowrun universe so appealing, so that's a good thing.
The book covers what's going on with the nanite-virus (and it's Shadowrun, so theories abound!), but also serves as part settings book and part deep shadows book. The settings chapters focus on Manhattan, whose power structures are in flux. Players who ran through season 3 of Missions will recognize callouts to various runs, which I thought was a nice touch. Additionally, there are various ideas and rules for extractions, which are probably the second-most common type of run out there, after simple theft. The usefulness of this section is probably campaign-dependent, but if you run the "standard" array of Shadowruns, extractions will certainly come up at some point.
The crunch that is in the book (a few drones, some new vehicles and vehicle mods, and drugs/toxins) is handy, but no one would mistake the level of crunch is this book with the 5th edition's Street Samurai Catalog.
Overall, the writing is very good, probably the best writing I've seen in a 5th-edition product. The mood of Jackpoint (a loosely affiliated group of successful Shadowrunners) is dark, sometimes panicky, and it's conveyed very well.
[4 of 5 Stars!]