Played about an hour of this so far. I was due to play more with a Warhammer nerd mate of mine but co-op isn't available until a certain amount of missions are completed. So that will have to wait. Plus, official launch is this week and all stats will be wiped, so I will just be playing to learn the ropes for now.
I had hoped I could play this on the couch via Steam link and Xbox controller but at the moment only the Steam controller is supported, which is annoying. I tried using the Xbox controller but the button set up is too fucked up.
Gamewise I'd describe it (lazily) as Diablo in space. The lore is extensive, as 40K has been around since the late 80s as a table top game.