granny: A few words on the single player: the campaign, as fun as it is, lacks a good deal of narrative urgency, because it uses a 'pick your mission' system. Something dramatic might happen in the story, then you can forget about it for days of in-universe time whilst you do something else.
I really love how they realized this in Dawn of War 2. There's a massive, system-wide infestation of Tyrannids (They're what Blizzard took from WH40k universe and called it 'zerg' - it's fundamentally the same race,) and with every mission you do - it doesn't matter whether it's a side-mission, or a 'main' mission - it takes you one day, and during that day, infestation of every planet in the system increases. You can actually do side-missions and capture certain points to decrease infestation (however, if you choose to capture the point, an installation to be more precise, you will lose access to another installation that might help you in another fashion,) and based on how well you do in missions, you can get another deployment (the game keeps track of stats like kills, time taken to complete mission, losses - basically, if you stomp your enemy into the ground, you get one or even two more mission per day.)
Basically, the game constantly keeps you under pressure, whatever you do. I would just really love the infestation to have bigger effect than difficulty of missions on infested planets.