I have to admit, I like this book.

first off - details are awesome. Up 'till now I've sort of been stealing ideas from other space/sci-fi oriented games to fill up the Expanse. Edge of the Abyss gives some excellent background material on various worlds and some interesting suggestions for endeavors based on those star systems. additionally, there's some (brief) details on the various imperial factions involved in the sector (they left out an endeavor for the mechanicus faction), some thoughts on sorcery (still no idea how to mutate ships in service to chaos), and a couple write ups on key Rogue Traders in the sector, along with their flagships.

Overall, I like this book. It goes far enough into details without being overbearing and/or oppressive in it's presentation. there's enough there to build a fairly good campaign without feeling that you're locked out of building your own stellar cluster and/or plot lines.

I would like to have seen more details regarding chaos reaver ships in the Expanse. I'd also have liked more details on the Yu'vath and their technology. However, I can (and will) certainly just make up rules on that for my own campaign so it's not that big a deal. Also, there's more than enough details in various/sundry Dark Heresy products to allow for all sorts of cross over potential. At some point i'll make a stab at converting some of the chaos rituals/sorcery material from DH into Rogue Trader, but my campaign is fine for now as it stands.

My suggestion/recommendation - get this book! it's well worth the expense, it gives you a LOT of ideas on where to go with the Expanse and what you don't find, you can use details here to springboard yourself into a reasonable guess.