This book is the second part of the ruleset conversion of Fighting Fantasy gamebooks into a role play game. This book actually covers *part* of the ruleset, but you need the first book (Dungeoneer) to play. On top of this, Dungeoneer + Blacksand actually cover the "first edition" Advanced Fighting Fantasy ruleset, while nowadays most players use the "second edition" ruleset.
So why buying this book? Because in the second edition ruleset the adventure in Blacksand, that covers more than half the pages of this book is not present! Blacksand is one of the cities of the world of Titan that most impresses readers (starting with "The City of Thieves" gamebook) for its flavour and atmosphere and having a (fairly long and developed) adventure in it is pretty useful for a game Director. On top of this, the book can be found second hand quite cheaply and for such a small price the likelihood that almost half of it won't be extensively read and used is not a drama, so take what is useful and leave aside the rest!
Ok, first of, don't get blacksand unless you already have dungeoneer. On its own it makes no sense whatsoever. With it, however, it's a good sequel. Several new rules now exist, mainly to do with being a priest and using 'priest spells' such as consecrate and summonings. After this is a section on Port Blacksand, followed by the adventure.
The adventure is very dissapointing. It lacks the indiana jones style excitement of Dungeoneer's two adventures, being a whodunnit where the heroes traipse around the city trying to find who's responsible for a murder, followed by a very short climax involving some evil priests and a brass golem. In truth, it sorely lacks, especially since RPGs are rarely played any more, however it still holds in it plenty of inspiration for writing your own FF adventures.