There is nothing unepic about Warhammer 40K. The franchise is practically synonymous with the word "epic." So it's safe to assume Warhammer 40K: Space Marine will carry on that same feeling, even while players control one Marine instead of entire armies.
We already know the premise of the Space Marine game by now -- Orks, Chaos, the usual business. But there's more to storytelling than the story itself, as Relic points out in the newest developer diary. Obviously we understand this, as gamers. The video offers a look at some of the more exciting scenes from the game, accompanied by bits of the soundtrack. As Relic points out, this is one of those few times they get to work with a real orchestra.