1. The raptors in this story are just normal Space Marines with jump packs. In every other CSM Story I've read, Raptors were mutated, grotesque things and I thought this to be the definition of a raptor! Is this up for interpretation?
Some Raptors are like that but not all. Just because one group of Raptors is a degenerated cult of monstrosities does not mean that another group automatically is. It's all about the amount of time they are exposed to the Warp and many other factors. Besides Captain Rhodaan and Squad Kyrith are Raptors of a sort, but not the same roving warband-type as Lucoryphus and the Bleeding Eyes in ADB's Night Lords trilogy. Rhodaan and his men are more like the jump-troops of the Grand Company that have taken the designation Raptors because it fits.
2. The Iron warriors despise mutation? Again, in Storm of Iron and several other Iron Warrior short stories, they were seen with Chaos war engines, Khorne Beserkers and other stuff. And the goal of the Warsmith in Storm of Iron is to become a Daemon-Prince! Has the fluff about them changed in past years?
Older book, older lore and again just because that group accepted mutation does not mean another has to. Honsou and Barban Falk were fine with having mutants, berserkers and other such rabble in their ranks because they didn't care. Andraaz and Rhodaan do care, they want purity in the ranks and do not want to command rabble. And as for Daemon Princes, comparing them to mutants is madness. They are two COMPLETELY different things, one is immortality and unlimited power, the other is deformation and genetic weakness.
The first half of the book has left me disappointed: I expected some epic batttles of hundreds or thousands of CSM against orcs. What I got are 64 Space Marines who don't seem chaotic at all, the only thing they do which seems evil is plotting against each other. Ok they tread their human population like shit but I've just read the fantastic Iron Hands novel Wrath of Iron, in which the "good" SM aren't the nicest guys either....
Where would the fun in that be? Then the battle would be a forgone conclusion and it wouldn't at all challenging for the Iron Warriors to mop up the Orks and it would make the slaves in the story pointless. The 3rd Grand Company may not embrace Chaos as open-handedly as some others but that again is all down to the recurring Warhammer 40k theme that just because one group, e.g Honsou's warband, does one thing does not mean another group must do the same.
And what the hell do you mean not enough evil?? In the first few pages Rhodaan orders a slave dunked into a cauldron of molten metal because he said the word God-Emperor. And Skintaker Algol who always wears a fresh covering of slave skin, still bloody, over his armour. And their callous abandonment of janissary troopers and slaves to the Ork hordes and their execution of any slave who even looks the wrong way. These guys are plenty evil.