The Delta Quadrant Sourcebook begins with a map like the three books in the series, but not an actual map of the Delta Quadrant, or even of the territory encompassed by the Borg Collective. Where the other supplements in the series have maps of their quadrants, the Delta Quadrant Sourcebook begins with a series of maps showing the flightpath that the U.S.S. Voyager took to get home. It shows an incredibly narrow slice of the Delta Quadrant, but so it should, and so too, does the Delta Quadrant Sourcebook. What this reflect is the fact that although U.S.S. Voyager undertook exploration during its journey home, it was never its primary objective. In fact, exploration was secondary, or even tertiary to its prime objective. Consequently, its encounters with cultures and species and worlds and spatial phenomena was fleeting, lacking the time that scientific rigour would otherwise demand. Thus its reports and analysis can only be seen in most cases as the initial cursory examination of a probe exploring a new region. This is highlighted in one of the pieces of colour fiction in the book and what it means is that once a Game Master has got her Player Characters and their ship to the Delta Quadrant, there is huge scope for her to develop her own content and even change details about a species or culture or a world because Star Fleet knows so little about the Delta Quadrant.
Unlike the earlier Beta Quadrant Sourcebook and Alpha Quadrant Sourcebook, the Delta Quadrant Sourcebook is not as easy a supplement to use in chronological terms. As it depicts an area of space between 2371 and 2379 and given its distance from Federation space, it is difficult to use in the Star Trek: The Original Series or Enterprise eras of play. Options are suggested, but there are far more of them set in the Star Trek: The Next Generation era. The overview of the various species, from the Devore Imperium and the Haakonian Order to the Vidiian Sodality and the Voth, taking in the Hirogen, the Kazon Order, and Species 8472 along the way varies from entry to entry. The length of entry is determined by how many times the U.S.S. Voyager encountered them, thus the Devore Imperium is given a mere half page, but the Hirogen, the Kazon Order, and Species 8472 over a page each. There is good, solid detail here, but it is let down by the lack of art. Only the Hirogen and Species 8472 are illustrated, whilst the rest are given a physiological description and given that they come from a visual medium, this is not really enough. There are descriptions of some of the worlds visited by the U.S.S. Voyager encountered as well.
Over a fifth of the Delta Quadrant Sourcebook is dedicated to the Borg. This includes an examination of who and what the Borg are, how they and their Queen function, how a species in danger of being assimilated might react, and so on. There are some interesting ideas here, such as the potentially immoral option of treating the Borg as invasive vermin, a threat to flee from, and as a viral infection. Another is restricted to worlds with cultures or resources which the Borg has deemed suitable for assimilation. If not yet technologically developed, a culture might regard the Borg as gods who will make the worthy immortal or demons who will steal the unworthy away... Types of drone are detailed, including maintenance, medical, tactical, and adjuncts. Throughout, there are in-game reports from the various governments and polities of the Star Trek universe. For example, the Cardassians are interested in making contact with the Borg Queen, the Dominion is wary of them, and Section 31 of Starfleet are still concerned about how much of a threat Juan-Luc Picard represents following his liberation from the Borg as Locutus. All of these add flavour and opinion that can help the Game Master portray these interested parties in her campaign. In this way, the use of the in-game fiction in this way is far better than has been in other supplements for Star Trek Adventures. In terms of worlds, the supplement is really rather clever. Instead of naming specific worlds, it examines the types of worlds that the Borg Collective is interested in. This enables the Game Master to create some interesting settings for encounters with the Borg, such as aboard their technologically advance floating platforms in gas giants or in the forcefield-protected facilities of demon worlds.
Under Lifepath Options, the most notable addition is that of the Liberated Borg. This is given as being for the Star Trek: The Next Generation era only, representing when they are a more frequent occurrence. This is not to say that they cannot appear in the other eras, but this is not really explored in the supplement. For the player Character, the Liberated Borg is a treated as a Mixed Species character and must have the Borg Implants Talent. This gives the Player Character three implants such as a Critical Array (interlink Node), Cybernetic Arm, or Ocular Sensory Enhancer. Their presence hampers social interaction as much as they grant technological advantages, but they can be removed. This takes a story milestone for each implant and only once all three have been removed, can the Talent itself swapped out.
Other species for the Delta Quadrant presented as fully playable characters include the Ankari, who use the energy from a nucleogenic lifeform to power their starships, the administrative specialist Jye, the Monean who live on a massive waterworld and are good swimmers and as former star nomads, also good navigators, the Occampa, and more. The guidelines suggest how the character generation process of Star Trek Adventures can be used, adjusted, or simply renamed to suit the Player Character.
For starships, the Borg feature again, with write-ups of Borg Octahedron, the command and control vessel for the Borg Queen and the Bog Torus which handles construction, along with the Borg Probe Ship and the Borg Tactical Cube. The Delta Flyer built by Tom Paris is detailed again, but more specific Delta Quadrant starships include the Kazon Raider, Hirogen warship, the Krenim Timeship with its time manipulating technology, Species 8472 Bioship, and many more. Stats for numerous NPCs are also given. Most of these are generic and unnamed, such as the Talaxian Smuggler, Occampa Explorer, or Hirogen Hunter, but there are named NPCs given too. These include Annorax, the Krenim officer and temporal scientist who turned the manipulation of the timeline into a weapon of war; Hugh, the Borg drone rescued by Starfleet; Commander Elizabeth Shelby, who became a tactical expert on the Borg following the battle of Wolf 359; and the Borg Queen. Perhaps the only NPC missing here is Rudolph Ransom, the captain of the U.S.S. Equinox, who used Ankari technology which drew power from nucleogenic lifeforms, to fuel his ship. Given that the Ankari are included, it seems odd that he is not.
The last part of the Delta Quadrant Sourcebook is dedicated to encounters, both the Borg and with other species in the quadrant. These all make good use of the details presented throughout the supplement. They including being caught at an outpost when a captured member of Species 8472 escapes and begins picking off victims one-by-one; Annorax, the Krenim officer and temporal scientist, seeking asylum with the Player Characters’ vessel; helping with a mass planetary evacuation ahead of the Borg arrival; attending an auction for the means to hack into the command structure of the Borg Collective, but the means turns out to liberated drones; and several more. There is discussion of possible ideas for Delta Quadrant-set campaigns, including a more swashbuckling style with non-Starfleet Player Characters, and also of the dangers of running a Borg-focused campaign. This is primarily because the Borg remain one of the most dangerous threats that Starfleet has encountered and going toe-to-toe with them is likely to end in death, disaster, and assimilation. Instead other means of defeating them are explored, typically involving either reprogramming the Borg systems or hacking into them.
Physically, the Delta Quadrant Sourcebook is a decent looking book. It is generally well-written and decently illustrated—though not always effectively—with a fully painted images. With so many species to illustrate, this is definitely a supplement which needed more artwork—and needed more artwork with good reason. It does need a slight edit in places. The layout is done in the style of the LCARS—Library Computer Access/Retrieval System—operating system used by Starfleet. So, everything is laid out over a rich black background with the text done in soft colours. This is very in keeping with the theme and period setting of Star Trek Adventures, but it is imposing, even intimidating in its look, and it is not always easy to find things on the page because of the book’s look. The other issue is that the none-more black pages are easy to mark with fingerprints.
Throughout the supplement, the descriptions and game content are supported by a series of in-game documents, reports, diary excerpts, and the like. Some of these feel a bit too long, but their focus, as with the book as a whole, on the Borg and the Delta Quadrant, means they too are focused and better for it.
If the Gamma Quadrant Sourcebook was three books in one, covering the Dominion, the worlds in and around Dominion space, and the Dominion War, then the Delta Quadrant Sourcebook is two books in one. One of them focuses on the Delta Quadrant and the other on the Borg, and with such two narrow foci, the supplement feels all the better for it. The supplement presents only a narrow strip of the Delta Quadrant, leaving vast swathes of space for Game Master to develop of her own, and that is even before considering adding the Borg. The Borg content will, of course, be useful throughout the Star Trek: The Next Generation era of play, but whenever or wherever she decides to bring the Collective into play, it should done with care lest the Player Characters be overwhelmed and outmatched. Overall, the Delta Quadrant Sourcebook nicely brings a slice of Delta Quadrant space to life and launches the Borg Collective as a formidable foe for Star Trek Adventures.