You'll be a Librarian, with all the power a Psyker can command.
Space Hulk is one of the best ideas ever to come out of Games Workshop: you crawl around in the belly of the interstellar beast, heavily armed and armored, fighting for your life again and again as the Genestealers claw out your innards with brutal ferocity. Space Hulk: Deathwing - not to be confused with tactical strategy PC, Mac and iOS game Space Hulk - is an attempt by Focus Home Interactive and Cyanide Studio to give the series an FPS variant, in which you play as a Dark Angels Deathwing Librarian, stalking the halls of a Hulk bringing the Emperor's vengeance to its unclean corridors. The trailer doesn't give much away, but then that's the whole point of a teaser; no doubt more will arrive soon.
This is a skills tree system, in which your victories grant you Fervor Points to spend on upgrades. As a Psyker, you also have special Warp powered abilities to use against your foes. You'll be searching for lost tech and relics, which you can use for the greater glory of the Emperor, slaying Genestealers left and right. This is the same team that made EYE: Divine Cybermancy, so expect oddness, but then oddness is pretty much what the Space Hulk universe is all about.