Ristin's Campaign Construction Center
The general problem with a Deathwatch game appears to be how to stop the players acting like space marines and solving all problems with superior violence…but considering this is the very nature of the Deathwatch system that could be problematic.
Other than interlinking with Black Crusade two main ideas spring to mind for a Deathwatch game.
The first is “an Inquisitor’s elite retinue”, the second is an odyssey style game with a squad of marines cut-off from friendly forces and having to battle their way through and then travel back to their home base.
The inquisition support game basically writes itself, but could be used to delve into the pre-screwed background of the Grey Knights, i.e. 2nd Edition Warhammer 40k. Actually in general the background provided for the different races went downhill after 2nd Edition…in my not so humble opinion.
The odyssey style game would revolve around the journey home, possibly resolving problems along the way, possibly also some ‘quest’ element seeking out then returning with a chapter relic. The relic angle could be useful to explain why the marines couldn’t just warp home the moment they find a ship. Possibly a prophecy is involved, with forces of the warp battling to thwart the quest, and the marines being tempted by the lure of chaos.
The inquisition game (or a “normal” game) would have a distinct reset-between-missions feel. The odyssey game (or a Black Crusade game) would see issues like spare parts, ammunition reloads, and replacement equipment become a critical concern.