Very few times in your lifetime do you ever come across a group of talent that has committed so much to a property that brought something special to an already great product line. Originally a source book for Call of Cthulhu, Delta Green had the honor of being the Origin award winner of best game in 1997 and ten years later, I have very little doubt the team at Arc Dream will do it again with the Handler's Guide. This GM-oriented source book provides backstory, rituals, secret history, and much sought after continuity up to our present day in 2017 for what our secret government conspiracy has been up to since it's disbandment in the late 1960s and back to it's reactivation in the 2000s. There is a permeation of writing throughout the book that has you feel as if you are reading a declassified document that is written with such confidence in itself that it's hard not to get sucked in.
Simply put, this is an incredible book. The materials proffered to the Handler are significant. Details on important figures throughout the agency's storied history, rituals that agents may come across in the field being used against them (or, in a dire case, by them), history that allows you to plan your scenario or campaign, and tons more. If you had ever been a fan of the Delta Green property, you would do yourself a disservice by not having this in your collection for the materials within. Even if you are not a fan of the setting (though, how could you not be?), this is a well-written and well-presented book that has a place on anybody's shelf if you have any interested in running a conspiracy based game at all.
The art? There's absolutely everything to say about the art by Dennis Detwiller. Each piece providing thought prompt of what unnatural and unearthly phenomenon wracks the depicted. It's gorgeous, thoughtful, and can be terrifying to some. The best way to describe it is that it fits with the game and the setting.
In conclusion, great book, worth the price, and certainly worth the 1d10 SAN loss.