To be fair to the author, the biggest problem I had with Angel of Fire was my mistaken assumption as to what sort of story it would be - to be fair to myself, this mistake could have been avoided had the blurb on the back of the book been more accurate. After parsing the blurb, I was under the impression that Angel of Fire would focus upon Solar Macharius: a general who conquers planets for breakfast, and who bears the weight of the universe on his shoulders. I liked the idea of reading about a strategist in the Warhammer 40,000 universe, rather than a warrior - but alas, what I found was the reverse. The story opens with a framing device not too dissimilar from that King employs in his books about Ragnar Blackmane or Gotrek and Felix, which makes it clear that the main protagonist will actually be a fairly normal Guardsman named Leo. Macharius is only seen fleetingly for the first half of the novel, which consists primarily of tank battles and the occupation of a hostile city; when Macharius eventually joins the main cast of characters for good, the plot proceeds with a 'trapped behind enemy lines' sort of scenario, rather than the 'overseeing everything from a command bunker' I had hoped for. Basically, I would have been very happy to read a book about Macharius where he never actually comes face-to-face with an enemy; instead, he comes away with a body count to rival that of Hot Shots Part 2. Similarly, I wanted a hero who used ingenious sci-fi strategies to rout his enemies; instead, Macharius basically saves the day by virtue of stealing something that seems insignificant but turns out to be very useful.
Despite not being what I'd hoped for, the book wasn't bad - if you're looking to see some Imperial Guardsmen engage in a variety of 40K battles, from armoured blitzkriegs to underhive gunfights, Angel of Fire delivers a decent quantity of a decent quality. There's some nice banter at times, too, with fellow Guardsmen affectionately ribbing one another - my personal highlight was the appearance of one nameless tech-adept, who only gets a few lines but utilises some excellent machine-analogies for talking with normal humans. However, as a story it feels more like a prologue than an actual novel - Macharius himself is far too perfect to require a character arc, and Leo might get a promotion but the narrative doesn't give him any conclusion more satisfying that blasting some folk with a shotgun. Indeed, the story ends very abruptly, without resolving any of the issues hinted at by the framing device (the very first page mentions an Inquisitorial report "pertaining to the proposed canonisation of Lord High Commander Solar Macharius and to the investigation of former High Inquisitor Hyronimus Drake for heresy and treason against the Imperium"), and giving most of the characters nothing to do save for basking in the glory of Macharius. Sometimes, the first book in a trilogy can feel a bit lightweight as the author holds matters of greater substance back for the subsequent stories; however, it can also be a result of the writer simply not telling a very interesting story, and I doubt I'll ever take the time to read on far enough into this series to find out which is the case here.
Overall, this is a tough novel to recommend - devout 40K fans and die-hard treadheads might glean more enjoyment from this than I did, but I'm sure there are plentiful books of similar tone and equal or superior quality. Indeed, I moved on to Guy Haley's Baneblade directly after finishing Angel of Fire, and (although I am only halfway through it) I would recommend the latter over the former. If you don't intend to subject the plot to any scrutiny, and just want to read about unnamed traitors getting lasgunned down and chainsworded in great numbers, you'll get a good dose of that here - but more discerning readers should avoid this like the Mark of Nurgle.