Fortunately for me, I was wrong. While not as good as, say, Dan Abnett's "Gaunt's Ghosts" series, it's a solid workman piece of 40K fiction.
Taking its cue from the first installment of the Dawn of War video game, the omnibus follows the Blood Ravens and their Captain of the Watch, Captain Gabriel Angelos. Plagued by doubt and strange dreams after having called in an Exterminatus of his home planet of Cyrene, he is charged with helping another planet, Tartarus, from orks. That leads to a full scale against other forces and the destruction of that planet in a warp storm.
Further events take him to other planets and threats from Chaos, Eldar, and even necrons.
As I said, it's pretty workman. It's not bad, by any means, and it doesn't feel kind of pretentious despite a lot of Eldar in it like it might have. It's entertaining, at least, if not completely enthralling. I wouldn't recommend it as a first read if you're just getting into the 40K arena but if you've played the game, or are just looking for more to read in the 40K universe, it's worth a look.