DH info from stream
You start as a Acolyte and become a Inquisitior LATER in the game. Edit: Valeria said "you can become a inquisitior, but you start as Acolyte." Then starrok reinforced it that you start as Acolyte.
The party size still 6 total. No change from Rogue Trader.
The power scale is lower than Rogue Trader
Story primarily about the Tyrant Star, learn about it.
Mommentum is gone. Morale system instead. You can build around the morale system.
Morality system. Radical/Puritan axis.
Less flat maps, more vertical maps. Changes to the engine.
Changes for the archetype system , a lot of changes. Improvements to make less overwhelming than rogue trader. No dumbed down the system.
Fully voiced game. Starrok said that dialogue still the same as Rogue trader.
Shorter game than Rogue trader.
Romance are in the game. Roughly as many as Rogue trader.
One of the Origins from Rogue Trader is becoming a Archtype in Dark Heresy (Psyker probably)
Aaron Dembski-Bowden, author of Night Lords novels, is writing a tie-in novel for the game's collection edition.
Updated models and animations.
Ship about the size of the Ebon hawk.
Similar co-op to Rogue trader.
A investigation system that flow with the whole game better going to be replacing the Colony/Trader empire management from RT.
A cameo from Rogue Trader confirmed.
Same people behind Rogue trader's OST working in Dark Heresy