Give him a gothic-pattern terminator armor.
Leaf gold, runes, little chapels, and all that other bling, but chaosified from 10,000 years of heresy.
Make his crux shoulder a bizarre merge of all four chaos marks, and put some naturally grown bone spikes on his other, with the helmets and shit on. Get rid of the orky trophy rack.
He should be in a more fluent pose, like's he's striding purposefully towards someone, and is just getting ready to stab someone unlucky in the gut with his huge sword.
Ditch the top knot, and give him a very organic, merged helmet, complete with a huge, fanged mouth, or make his face all melted and scarred. No matter what, he only gets one eye, and where the other would be, it's all warped, and has a huge demon rune.