From what I've seen and played (the closed testing) it's 'okay'.
Most of the lore appears spot on (Redemption Bolter please take a seat outside) and some of the details inside the ship like dead Ad Mech personnel, purity seals with readable catechisms/litanies etc is a great touch.
But I don't feel that it is as good as Space Marine was. Sure, I know you're on a Space Hulk in mainly cramped conditions in Terminator Armour ... but the atmosphere doesn't grab me and smother me like AvP did or combat feel to flow like Space Marine did.
Sounds really disappoint with the Storm Bolter sounding less lethal than a 9mm pistol does in many games.
Graphically, aesthetically, detail-wise and lore-wise - They really have done a rather excellent job.
Feel, atmosphere and that certain thing that grabs you and doesn't let go in a great game... they're just not right or just not there for me.
And yes, I am actually currently reading Death of Integrity by Guy Haley.