I spent a good part of the predecessor, Scar Night, trying to decide whether the book was fantasy, or SF disguised as fantasy. There were indications of the latter, with 'angels' having fallen from 'heaven' in a technologically advanced vehicle ('the Tooth'). This book, however, steams ahead with straightforward fantasy approach, if with more engineering than usual.
Scar Night was very much about the hanging city of Deepgate, and one of my criticisms was that the city, while intriguing, was poorly described. I felt the story was intriguing despite that flaw. This second book is very much about hell/the Maze/Iril, and the politics of both hell and earth. Unfortunately, all of this is again poorly described. It's generally easy to follow what's happening in the main plotline, but hard to follow the geography of both the Maze and its connection with the earth. There's a similar problem with exactly how the whole soul mechanism works, though this is a key element of the story. The politics of the various infernal and earthly factions I found equally vague, though again it was easy enough to keep track of 'good' and 'bad'. Finally, there were a couple of jarring temporal shifts, though they were well marked with section breaks. All in all, unfortunate flaws that mar a quite interesting story.
All of the structural issues aside, Iron Angel fulfills much of the promise of Scar Night, if in unexpected ways. The focus shifts from Deepgate to Dill and some other characters, as they become enmeshed between gods (Ulcis' brothers) and darker forces. I personally found the story less interesting, not being a fan of military campaign fiction, but it was well laid out, and there's more than enough human, personal matter to keep character-oriented audiences going. It's unclear where the story will go next, which I count as a good thing, and I look forward to a lot of solved mysteries and tied ends in the last book of the trilogy.
All in all, a reasonable if not stellar steampunk fantasy, and one that gets points for an original environment and story. Worth continuing from book one, if you can put up with a little vagueness.