Nice work, i think for me when i look at busts like this i want to see lots of intricate detail. Looking at yours i find some areas particularly flat, such as the skin and helmet. Like it could do with some colour variations like some glazes of yellow for light being picked up on his helmet and possible some more weathering, for his skin i would try and put vein details or make it seem more realistic anyway. Like you've done with the leather, that looks suitably leathery if you get what i mean. Nice job tho, not something i'd ever paint but still nice.