It's. So. Good.
The Blood Sea is an exceptionally cool part of Ghelspad (who's not into an ocean that's literally poisoned by the blood of the titanic monstrosity imprisoned beneath the waves?) and its corruption adds a uniquely Scarred Lands twist to the challenges and tropes of seafaring. So obviously I was excited. I mean, there's a big tentacled octopus that might be made out of blood on the cover.
That cover is a promise, and the book fully delivers.
Of course, it's extremely cool. The thought that's gone into how the nature of the Blood Sea affects sailors (especially low level characters) is excellent, and the subclasses based around its corruption definitely spark the imagination. It's easier to imagine some of them as NPCs than as PCs, and some example stat blocks would have been much appreciated, but however much mental gymnastics it takes to work in a PC who single-mindedly devours gobbets of decaying titan-flesh as a source of power... I'm down.
Blood Sea is also pleasingly functional. The background on crew roles and duties is light, informative, but easily digestible. In a few minutes, a GM can figure out supporting characters and crew politics - and answer the useful question of "ok, but what does my character do all day?". I really could have done with this book when I decided to kick off my last campaign with a shipwreck.
The NPC factions and crews do well at putting meat on the bones of all the suggestions the author makes throughout: they present a good range of crews, with different compositions and ambitions, and there isn't one I couldn't see myself picking up and throwing into an adventure. My favourites, it has to be said, are the mysterious fae-touched crew, and the Sea Hag. Always here for hags.
There are a couple of minor issues: another editing pass would have picked up minor errors (there's a dreaded "page xx" on pg. 10), and maybe tightened up some phrasing here and there, but these are trivial and in no way affect the quality of the book. If you're looking for crunch - sea combat systems, ship maintenance and the like - this isn't the book for you (though the ship maps are useful), but for setting, story and inspiration it's first class.