Rock Paper Shotgun have some more info on the upcoming Battlefleet Gothic: Armada game.
Briefly, the game will depict the struggle for the Gothic system. The game starts with the Imperium controlling the entire system and struggling against invading Eldar, Ork and Chaos forces. The game is dynamic, with fleets and ships being built and moved on a turn-based battle map before the game turns into a real-time tactical mode. The single-player campaign will only feature the Imperium as a controllable faction, but there will be skirmish and multiplayer mods featuring the other races. The game will also feature the ability to level entire planets from orbit (the dreaded "Exterminatus" order) and the AI of ship captains will develop, possibly leading them to rebel if you don't handle them right.
More info here.