This book redeems somewhat Nick Kyme's treatment of the Salamanders, possibly the most underrated legion/chapter. It is muddy at times and the whole Meduson story arc seems absolutely pointless (we get a third of the book on what is, in the end, a closed arc), but for the first time in the Horus Heresy series, we get a clear glimpse of the Salamander ethos and of their primarch.
Vulkan is shown, heard and followed, truly, for the first time. Vulkan Lives and Deathfire were exervises in frustration, filled with skippable chapters and "come on!" moments (as in "come on, this is ridiculous even for 30k"). Now, finally, not only does he live, but he also speak. Oh, what a glory it would have been to see more of him, the way we get Robby G or the Lion. But no, after what amounts to about half a book, he gets a permanent "position" and it's unlikely we will get to see him from now on, more than once at least.
It's like the HH writers met and passed on some story arc dregs to Kyme, asking him to finish them off. He did a much better job in this book, and we actually got to see some exposition by actions and setting rather than telling. The book is still weak, particularly in the story arcs part, but for the first time in Kyme's 40k history (and unfortunately I have read most of his books), there are individual parts/chapters that are truly enjoyable to read.
To be concrete: the adventures of the wacky primarch and his 3 sallies, except some murky stuff with some dark eldar (which do not amount to much action), are ok. Even some Meduson scenes are well done. The reunion with Dorn and the final parts as well.
The villany of Marr, the whole Iron Fathers parts, the pointless back and forth on Meduson, the space battles that amount to nothing, a whole bunch of characters introduced clearly only for Kyme to have someone to finish off, those parts are less fun. The eldar trickery is absolutey dull.
All in all, better than anything on Vulkan written before. Too bad it's probably the last one we'll get and too bad the Black Library writers have this "only one primarch per author" thing (except Abnett and McNeill of course).