A couple of months ago, me, Rebecca and Erik/Nordic had a Primaris-off! We decided to use a Primaris Marine from the Dark Imperium box and convert it to our own style. But all of us had to convert and paint miniatures for Tor Megiddo, so the others aren't finished yet. I'll make a post with all the Primaris miniatures when the others are finished.
I wanted my Primaris to still look like a Space Marine, so I didn't convert it much. I just sculpted a few creepy faces on the armour, and gave it a new sword and helmet.
I painted this guy really quickly, but I think it turned out good. The armour was painted by drybrushing several metallic paints over it, and glazing/shading/blending the colours together with sepia and orange shades.
I primed the miniatures before the crackle-paint on the base had dried, so the base lost a lot of texture. I tried fixing this by painting texture on the base, which actually turned out great!