The Extraterrestrials Sourcebook collects previously published information about the alien races at large in the Conspiracy X role-playing game, and then brings their activities up to date with the new oughties timeframe. That said, the book is very rooted in the past. Each of the three chapters goes deep into the history of its species. “Way back, before you were born”-deep, to the origins of each species. Which is great for the long view. Midway through the Saurians chapter, I started asking myself, “Is this all we’re going to know about what they’re doing now on Earth?” Atlanteans, Greys and Saurians do all have a section on what they’re up to at the moment, but it’s so tantalizingly brief and vague compared to the full, detailed histories of the three species.
A lot of that must come from the original remit of The Extraterrestrials Sourcebook: condense material written for supplements of the first edition of Conspiracy X into one volume for the current line and move the timeline up by fifteen years. In light of that, each chapter does a remarkable job covering history and culture of three distinct species.
The name of the podcast escapes me, but I remember hearing the designer of Swashbucklers of the 7 Skies, Chad Underkoffler — I think? It’s been a long time since I heard the episode in question — describe his realization that long histories of how Sir Buffington defeated Lord Nemesis, and so on, can and ought to be elided into “Epic stuff happened leading us to this tipping point. Now you guys need to do something.” I’ve taken that to heart, and any time I run across supplemental material that is basically a long timeline of events that sound very cool, but are of limited utility to informing the present situation — unless you decide all those points on the timeline are covert plot seeds to bring forward to your game’s time frame — I do look askance, and wonder if this space could have been given to something a little more relevant to the contemporary status quo, and how it’s about to fall apart.
That said, I did appreciate the look into the culture and mentality of the extraterrestrials, different and varied as they may be. The Greys are the closest to monolithic, since they’re so deeply interconnected by telepathy. But even they have differences and internal division — especially, interestingly, between those on Earth and those on Greyworld. Greys on Earth are quarantined from the rest of the species because of concern about psychic contamination. The Saurians, it turns out, are divided into many factions, unlike their representation in the corebook, which is really just one faction that is most visible to AEGIS. And the Atlanteans wind up a race of radical individualists, as everyone strikes out on their own.
The Extraterrestrials Sourcebook is an interesting peek into the alien races interested in Earth. I’m dubious, though, how much use the information is here to 80% of the Conspiracy X games out there, as it seems unlikely most of them are going to go that deep into interaction with any one species, let alone all three. I’d rather have much more information about what they’re doing on Earth right now, and examples of how AEGIS cells and Black Book agents interact with them.
 Acknowledging that any throwaway mention of what an AEGIS cell did or reported is really a coded plot seed for the GM’s own campaign, either to kick it off or provide a template of what the players might get embroiled in.