Edge of the Abyss is a setting book for Rogue Trader, offering examples of the sorts of things you might find in the Koronus Expanse (the border region that is in the process of being conquered by the Imperium). It's kind of a tricky thing, really. The whole point of the Koronus Expanse is that it is largely unexplored and thus you can find theoretically find anything out there. To even have a setting book at all kind of undermines that idea. And yet, it's not like we GMs have infinite reserves of time and creativity. It can be handy to have a guide.
Edge of the Abyss probably comes as close as possible to striking the right balance. I could build a couple dozen adventures from the ideas in this book. Unfortunately, they would mostly be WH40K-style adventures and I have little interest in that.
Oh, look at me, being so snarky about it. There's really no problem with Edge of the Abyss. Maybe a little section where either the book or I am fundamentally misunderstanding the chronology of the 40K universe. One of the planets has ancient Imperial technology, which doesn't track with what I assumed was a fairly straightforward sequence of: 1 - Dark Age of Technology expands human settlement to its farthest limit; 2 - the collapse of that society leads to human planets losing contact with each other; 3 - The God-Emperor launches a crusade to reunite the planets that ends in an attempted coup by his lieutenant; 4 - the Imperium slowly expands into the areas the Emperor never got around to. Maybe there was a step 3.5, where the Imperium gained certain planets, but then later lost them . . . If so, this is the first I'm hearing of that happening in the Koronus Expanse.
But to harp on such a picayune inconsistency would betray a mindset that is going in to this book looking for something to complain about. The planet of Sheldon's Folly may just be an outlier. Maybe a colony ship just got lost in the warp. It happens. One of the sample tall tales is about a spaceship that wound up traveling 100 years into the past (whereupon, in true WH40K style, the crew is executed for impersonating naval personnel). A strict chronology of events is not something the setting has ever promised.
Which gets us to the crux of the issue. Edge of the Abyss is a pretty conservative take on the WH40K universe, and I'm still ambivalent about said universe. You land on a strange, alien planet, you find some mysterious crystal ruins, and surprise, surprise, the ghosts worshiped Chaos and now they're trying to drive you insane. Everything you find is cursed or tainted or heretical or just plain trying to kill you. It's exactly what you'd expect . . . which is kind of the problem. WH40K has a lot of good, interesting, and unique science fantasy, but it's wedded to a very narrow set of genre expectations. Rogue Trader in general pushes the envelope a little (most of the NPC Captains in this book are genuine swashbucklers, with very little horror, for example), but it's still the grim, dark future of the 41st millennium, and if there's not only war, there is quite a lot of it.
So we see the return of the same handful of alien species we've seen before. The Eldar get a little more detail, though I'm still not sure what a Maiden World is. Also Orks definitely have factories. That is confirmed canon. Which, of course, just deepens the mystery of their supply chains. Are there Ork accountants (I'm sorry, akowntanz)? And why, if you're going to give them ordinary jobs, did you even bother making them an alien space fungus? What is the point of it all?
Overall, Edge of the Abyss is not a book that I'm going to get a lot of use out of. I prefer a looser, less predictable version of Rogue Trader and will probably wind up diluting WH40K's trademark grimdarkness so much that I'll need to go entirely off book. But hey, at least my collection is nearly 100% complete.
Ukss Contribution: There's a star system near the entrance to the Koronus Expanse (because of storms in the spirit world, volumes of space can have entrances) that is just filled with "a multitude" of geometrically perfect, asteroid-sized spheres. The book tries to make them sound vaguely sinister, attributing them to an elder god (which doesn't sound automatically bad . . . but WH40K), but judging by the rules, they're harmless. I like to think that maybe they are the work of a forgotten god, and that he just happened to really like spheres.