Let me start by saying this is a beautiful product and I am proud to support the publisher with my purchase. However, this comes with an important caveat. Allow me to explain...
A beautiful cross section and overland map, coupled with concise and compelling writing by the author. A deviously sinister web of plot potential and all the deathly goodness one could expect from an OSR style campaign. Roll tables are also generously included for "room dressing", random encounters, wandering monster actions, and local rumors. In general this guide contains probably some of the best advice i've come across for running a sandbox/old school megadungeon type of campaign. Let's not forget the excellent world 'fluff' and flavor text, both for Gloamhold and the greater Duchy of Ashlar itslef. Which presents a nice compact area that players can retreat to, explore, and rest whenever the dungeon becomes a grind. Though, the megadungeon of Gloamhold itself is precisely where my expectations fell short.
The bad (Or possibly good):
Fluff, fluff, fluff! This entire guide is about 85% world fluff and flavor text. Nowhere is there a single dungeon map to be found (excluding the ant hill cross section). Instead, each broad section of the dungeon gets about a two page write up with rumor tables, key features, and a well written, albeit a somewhat repetative description of said areas. Perhaps it is my fault that I believed this was something I could use as an in game tool rather than purely pre-session prep. In fact, the Gloamhold Campaign Guide really just presents an overall set piece, with any actual structural substance still needing to be created by yourself as the GM. This could be a let down if you are expecting to see something akin to a sprawling labyrithine dungeon complex, a la Gary's Castle Grayhawk, Undermountain, and the like. Think of this book as more setting primer than an actual campaign guide.
To conclude, I appreciate the author's intentionally open ended design, and I understand it is impossible to map an entire dungeon of this scale (though something would have been nice). This is still a great source for inspiration, especially when considering the extremely modest price. Just know what you're getting into before picking up a copy.
[4 of 5 Stars!]