Like most of the Games Mechanics products, this supplement is largely about Crunch.
But it's very good Crunch.
There are four main chapters. Chapter One is a selection of new spells that could slot right in to an existing game. (The mechanics get a Laugh Point from me for the "Cellular Hand" and "Hand Gun" spells, which work just as you'd expect them to) Chapter Two is a variant magic system for lower-key, ritual magic. This lets D20 Modern break out from the "D&D with guns" pit and into the territory of more "realistic" occultism.
Chapter Three is an interesting look at how the military would adapt to different levels of magic in a campaign world, ranging from "rare and restricted" magic (with the occasional Special Forces Spellcaster) to "common as dirt" (with the fighter-mage style "Combat Grunt"). Chapter Four is a selection of FX focussed equipment.
If you use magic in your campaign and want to expand it, or would like to run a grittier type of magic than default D20M, then this is an absolute must-buy.
[5 of 5 Stars!]