I purchased this because I am beginning to plan a pirate campaign (and eventual DM's Guild products) set in the Sea of Fallen Stars. To that end, this book would be 5 stars and is perfect. But as a stand alone product set outside of the Sea of Fallen Stars, I think its a bit less useful, thus the 4 star rating.

The first couple chapters have some useful history and lore, and a bunch of edition specific rules around profieciency I didn't find that useful. The new spells do not seem worth converting to 5th edition.

Chapter 3 on Nations of the Inner Sea is very useful if you want to run a pirate campaign there, and gives an overview of every nation's relationship to piracy. Similarly, Chapter 4 on the Pirate Isles gives plenty of details and ideas to help build interesting adventures. Chapter 5 is a Rogue's Gallery, and I expect to use many of the pirates featured there, though many need some tweaking to make really memorable villians I think.

Chapter 6 and 7 are all about ships and nautical mechanics. That already exists in 5e in Ghosts of Saltmarsh, and I am not super interested in the mechanics, so I just skimmed these chapters and don't have much of an opinion.

Chapter 8 is an adventure. Its pretty well done in that there is a fair number of choices and branches the party can go down. But it would take a fair amount of work as a DM to actually run since its pretty light on details. But the hook and structure is probably good enough that I will use it as an adventure in my eventual campaign.

Overall, I got what I was looking for out of the book, but I think its pretty specific to "I want to run a pirate campaign/adventure". I dont think its really worth buying and reading on its own for fun compared to other setting books that are out there since it is so specific.