I'm surprised I'm giving this five stars myself, but Dan Abnett truly surprised me with his immersive writing style and the depth to which he gave what, on the outside, looks like your standard hack'n'slash. As much as I love the 40k universe I didn't expect to enjoy this as much as I did. 
 Do not get me wrong - the plot is still very hack'n'slash, but the combat scenes and those surrounding them are made interesting through Abnett going past the usual tropes of description, focusing on a range of details to bring the scenario to life. The worlds of the book feel much more real than they did in previous novels, and the decision to include moments of the main protagonist - Loken - reflecting with a remembrancer was a very effective method to showcase a more relatable side to the character than otherwise could have been shown. 
 As other reviewers have noted, Abnett also does well in giving each of the headlining names a distinct, memorable personality - something other authors of the Black Library have struggled with in the past, given the somewhat limited frame of development that Imperium characters have in comparison to other settings. I found myself sympathising with some and finding others almost irritating, which is always a good sign of a more varied cast than having a 'generally neutral' view to them all. I also felt he did justice to the legendary Horus and the introduction of the Sons of Horus which was something I was curious about. Covering something so integral to 40k lore was quite the challenge and yet Abnett wrote a novel that is the highlight of what I have read from the Black Library so far. 
 Definitely a recommended read for a newcomer to 40k, a veteran, or even someone who has no interest in the franchise but likes a bit of non-apologetic sci-fi action!