If you're even remotely interested in the Sabbat then you should seriously consider getting this guide, as the core rulebook *barely* touches upon anything more other than Sabbat being "perceived as mindless savages and bloodthirsty fiends." This book is vital for players of Sabbat characters (and Sabbat-using Storytellers), even moreso than the Guide to the Camarilla is vital for players of Camarilla characters since much about the Camarilla is already covered in the core rulebook (but the Camarilla guide is still a nice book to have).
Just about everything about the Sabbat is discussed in depth, like initiation, ritae and war tactics. Factions in the Sabbat are covered as well as individual political positions. A specifically-Sabbat method of character creation is presented and Sabbat-appropriate Abilities and derangements are also present. Many Sabbat character templates are listed, which are all extremely helpful (and pretty interesting). There are advanced Discipline entries, usually for ranks 6-9, as well as types of Disciplines not featured in the core rulebook.
New shades of vampirism are presented here (though due to their awkwardness / susceptibility to abuse, not all are recommended as being playable): the twisted Blood Brothers, the ominous Harbingers of Skulls, the bizarre Kiasyd and the vengeful Salubri antitribu, as well as the gruff Panders, the Sabbat's own brand of Caitiff (who seem to have more status in their sect than the Camarilla Caitiff have in their own). Also, there are all the Camarilla clans' antitribu - excluding the Tremere antitribu (who do get a mention, however), for pretty permanent reasons.
A really, really nice section takes up the burden of making Sabbat Chronicles something more than dice roll hack n' slash or rampant abuse of mortals and runs with it. It also talks about giving Sabbat characters greater meaning to their unlives than "the Camarilla hate you, so you must kill them" or any equivalent plot. I don't think it succeeds as much as it had probably hoped to, unfortunately - a lot of it borders on contradiction.
(On a side note, some of the art is very *explicit,* but not much. There's really only one picture that came close to challenging my will power to not disgorge my last meal. I certainly can't say the stuff illustrated therein isn't *appropriate* for a sect like the Sabbat.)