Hidden Lore was the collection of overflow material from the 2e core rulebook that was cut to achieve what was purportedly a Procrustian page count. The book says so up front and the contents consist of rotes, clarifications, some alternative rules, and a sample chantry that was bundled with the 2e Storyteller Screen. Part of releasing a book that consists of content that didn't make the cut into the core book is the wager that the worst material in a core rulebook is still better than the minimum standard that some set of fans have and for me the book did not make that cut. This may reflect years of storyteller experience as well as the embarrassment of riches that is having an additional 60 books or so that were published after this one.
The section on alternative play styles provided options for 1 on 1, bluebooking, troupe play, and troupe storytelling which were somewhat innovative at the time but in the intervening 25 years other games have run with these options and overall come up with smoother systems.
The combat simplifications are also acceptable for high energy chronicles where players need to wreck a wall of mooks and tries to replace the tradition four roles per character per attack to one. Again, other systems innovate on this better but at the time it was notable.
The descriptions of the Traditions rotes was flavorful but the sphere requirements may result in you knowing less about Mage at the conclusion. Also the systems presented are sometimes novel and other times ridiculous.
The Marauder and Nephandi rotes are somewhat less cringe-worthy but still present problems in terms of what spheres are called for and what systems are used to implement an effect but they are flavorful.
*The sphere summaries are intended as hand outs and restate what's in the core rulebook. If you're getting this digitally, copy-paste from a core book will do just as well without having to try to find a way to photo copy the sheets.
How to make interesting characters was almost painful to read as it was a mix of "you know, just do it" and "learn to portray attributes you lack" which was a bit uncomfortable.
The rotes present questionable systems with Prime 2 being required almost randomly and other spheres being involved for reasons I don't quite understand.
The Chantry presents a magick-dense Seattle that directly contradicts the later statements about how rare mages are unless one posits that Seattle is an absolute hot bed of mage activity for unrevealed reasons.
The door that leads from the earthly to umbral aspect of the Chantry has a roughly 7 percent chance of generating paradox which seems remarkably dangerous for something so regularly used.
The sections on the distilled view of each faction in the Ascension War should have been woven into the core book. Anyone who gets this will likely know it and anyone who grabs the core rulebook should have access to it.
The notable characters section is largely a collection of already released characters and no stat blocks which makes it almost useful.
Don't get this book if you have a fair number of other mage books and especially not if you don't have a firm grasp of the sphere system as the rotes may lead you astray.
[2 of 5 Stars!]