I said it in the other thread and I'll say it here. I hate the fact that it's been retconned from Corax tampering with the gene seed and messing up and making the mutants. I hate the fact that it's the Alpha Legion that were responsible for the mutants instead of Corax itself; and I hate the fact that the Emperor just gives Corax this information instead of using it to expand the legions closest to Terra to fight the whole I don't know...seven year galatic civil war thing. It has completely changed the Corax character and his shady dealings during the Heresy, which are entirely non shady now and the fact the mutants are the AL's fault also undermines Corax killing the Weregeld for me as I personally know he's not responsible for them. Also giving the the primarch template/gene seed deux ex machina solely to Corax makes little to no sense.
However the other spoilers sound rather interesting. I like the idea of Corax ripping the head off someone who beat a young girl in front of him, that combined with his leading a guerrilla war and leaving Deliverance as it was suggests Corax is up there with Vulkan in terms of being in touch with the 'common people.'