I finished this one up last night, so here's my review. WARNING: I cannot write a useful review without SPOILERS. Do not read any further unless you want plot details.
The story takes place on Shardenus, a pretty standard Imperial hive world. Shardenus has apparently turned from the light of the Emperor and the Iron Hands, a Titan detachment (2 Warlords, 2 Warhounds), and several Guard regiments show up to burn the place down. As a twist, it's revealed that the lower echelons of the world's population and military don't even realize they've turned traitor. There are Loyalist elements of Shardenus' Guard regiment who are killed by the invading Loyalists simply out of confusion and death-by-association.
The book largely focuses on a Mechanicum Magos, the Guard Supreme Commander of the Loyalist forces (Nethata), two loyalist Shardenus irregulars, a Death Cult Assassin, and an Iron Hands Sergeant, Librarian, Iron Father and Clan Captain.
When the plot begins, the Iron Hands are shown to be callous about the deaths of their "mortal assets," aka Imperial Guardsmen. Rauth, the commander of Clan Raukaan, orders thousands upon thousands of Guardsmen into futile efforts as a diversionary tactic. When the Guard's general complains or hesitates over the losses, he's threatened with execution. The recurring theme of the book is: "The Iron Hands are dicks." Seriously. The squad sergeant, Morvox, you get to learn about starts out with misgivings about such tactics, but he is berated by the Iron Father (the Iron Hands' equivalent to a chaplain) and threatened. See the theme here?
The book is superbly written, with great action scenes, vivid depictions of the scenery and setting, and interesting characters. Chris Wraight is a very talented writer, and I think I'll pick up some more of his work. What gets me is that the Iron Hands aren't really heroes in the story. With Ultramarines, Space Wolves, and even Dark Angels, you get a character you can rally behind and cheer. Uriel Ventris might be a Codex-breaking fool, but he does heroic things and you cheer his victories. Ragnar Blackmane isn't a humanitarian by any means, but he's so badass you can't help but love him. The Iron Hands as depicted in Wrath of Iron are downright despicable. You can't cheer for Rauth as he sends a million Guardsmen into the teeth of the enemy guns simply to draw a percentage of the traitor forces away from points in the wall. There's a scene about 2/3rds of the way through the book where Rauth lines up regiments upon regiments of Guard in an underground access tunnel to the hive. He commandeers both Warhound Titans into this fight as well. When the battle begins, the Iron hands push forward, leaving the Guard regiments in the dust to be butchered by mutants and daemons. You just can't cheer for that.
Much is made in the beginning of the book about how the Iron Hands slowly lose their humanity (or super-humanity, rather) as they replace their body with bionics. They lose all emotion eventually, operating purely on logic, numbers, and a sense of duty. There's a bit of a clash there, as how can you have faith in the Emperor and a commitment to duty when your emotions and sense of sympathy/compassion has been stripped away? It's a fun point to ponder.
Eventually, Nethata has had enough of the wasting of his men and materiels, and he colludes with the Princeps of the Titan group to stand up to Rauth and demand a change in tactics. Unfortunately, the stand falls through. Nethata dies. In fact, anyone in the entire book who shows one shred of humanity...dies.
The irregulars from Shardenus? One dies in a pointless charge against the enemy lines. The other is executed months after the siege is over as part of the Iron Hands' programme of eradication of all residents of Shardenus.
The Librarian who retained his mortal mind in order to be a Librarian? Throws himself into a warp rift to close it and is tortured for eternity by daemons as a result.
Nethata commits suicide after his plan falls through, because the Princeps he colluded with was executed by the Mechanicum for refusing orders (and colluding with Nethata).
The Death Cult Assassin blows himself up with an atomic bomb carried in his chest cavity in an attempt to destroy the daemon prince behind the whole invasion (he fails, by the way).
The moral of the story is that all mortal flesh is temporary, fleeting, and weak. The only thing that survives is iron, and that is all that matters. It's a fitting moral for an Iron Hands story, and the book as a whole is a neat insight into how the Iron Hands work. But you can't read it expecting any sort of final satisfaction. The characters you root for all die, and the characters that are complete dicks win the day. The book is well written, if a bit thin on character development and containing a couple plot holes, but it will leave you depressed and angry at the end.
I was actually dabbling with the idea of starting an Iron Hands allied detachment for my Ultramarines. But after reading this book, that's right out the window. Iron Hands? Those guys are dicks.