Do I need to tell anyone to buy this? I shouldn't have to. It's amazing. You should know that already. Fantasy Flight decks out their supplements with more options than a Baskin Robbins.
It starts with the obvious ship components, new hulls (Grand Cruisers anyone?), and weapons. If you don't love Nova Cannons that shoot warheads through the Warp before hitting their target, you don't play Rogue Trader. Then they add in a ton of backstory, life on a warship, and the history/status of the current Battlefleet Koronus.
For the GMs, there is plenty of detail on Xenos threats, rules for more detailed space battles (squadrons, damaging fleets, mustering your fleet, deploying forces, etc.) There are a lot of new mechanics here for the folks who want to really dig into space battle. That's me. I love the new options, multiple pregenerated ships to throw against your players or give to them, and of course Xenos scum.
It may be one of the shorter books at around 150 pages, but it also isn't too pricey. If you want more than just the standard ship battles or more options for you and your players to create the most dangerous ships in the fleet, then this is your book.
[5 of 5 Stars!]