Everything is hard biology/science (well, for GW). As Folomo put it, it's a cold, hard science taken to the point of magic. Nano-machine androids led by energy-beings which can manipulate gravity, etc. But they fulfill the "undead" archetype in 40K, essentially being an army of robotic skeletons accompanied by a energy/life draining "Star-Vampire".
http://www.blacklibrary.com/all-prod...nal-ebook.html
As it says in the summary, I only read the preview or a free extract BL were doing, but basically, a reforged Lord Celestant returns and gone is the pat on the shoulders, rousing speech before battle leader... now he's quiet, taking orders before striding off to fulfill them, rarely talking except to give commands and seems driven to kill. In the extract, when they reached the Realm of Beasts, they encountered some humans being chased down by Orruks, and sheltered the former and attempted to parley with the later, recalling Sigmar's alliance with the Greenskin God, how they could work together, etc. The dialogue is ended by the Lord Celestant, growing tired of the posturing, pulls his sword and simply hurls it to impale the leader Orruk's face!
Like I said, signs of psychopathy.