There is absolutely no reason for you to skip buying this if you love Rogue Trader.
This is the "Inquisitor's Handbook" style book for Rogue Trader. The better question to ask is what does it lack? Because it has so much material you will be inundated with possibilities. New advancements for all the previous Rogue Trader archetypes, new character types like Orkz and Kroot and tons of new gear for every character type are only the beginning. It contains expanded rules on starship creation, as well as, and this has been a long time coming, rules for iconic vehicles like the Rhino APC and Aquila Lander. Though the vehicle list is not as expansive as you would hope for a Warhammer 40k game, the vehicle rules are simple enough that you can reverse-engineer them to make your own vehicles well enough.
If you picked up the Rogue Trader book and liked it, this should be your second purchase.
[5 of 5 Stars!]