I've meant to come and crit this for a long time but life has conspired against that in some ways.
I must say, you should be happy with the design of the armour. It looks sensible and highly usable, whilst still being a fantasy creation. This is something I like. I also like that it is NOT another Spess Mehreen. Though: why a skull helmet? Isn't that a very weird helmet-design, when the rest of the armour looks so practical and unadorned? Unless that contrast is exactly what you aimed for.
You have good values overall. Maybe the face is lacking some definition and is in almost full profile while the rest of the body is 3/4 profile. I can't quite figure why it'd be that. Though it is obvious you aimed for a portrait-look. As said, the face could use a little more definition, with just a notch deeper shadows in places. As is, it looks oddly flat to my eyes.
I am also missing a shield design: that is one large area of nothing. Negative space to rest your eyes on is important in a painting, for sure, but that is a bit much, especially so when you consider the flat background.
And where are his legs? It's just a big black void there... I'd expect at least a hint of a glint of armour on one leg. The cloak also looks a bit unfinished to me.
I do like the technique you used and your sense of proportions and anatomy are solid, to my unrpofessional eyes. Nothing to complain about here, really. Maybe that the foreshortening on his left arm on the shield is a bit dubious, but I hadn't noticed that before I looked closer.
I think you should be happy, and perhaps consider topping off the things I pointed out, to make him complete?
You're really good at shading metals dude. So shiny and real and 3d. Well good at painting any textures really I just suck at metals so I admire how you do them. :<
My only critique is that the metals shading is higher in contrast than the rest. I'd put lighter highlights on the skin etc, to even it out- because it looks more washed out than the chest piece does. But it doesn't take away from the piece too much honestly.
I think you should be pleased, this looks really good.
I love the work you did on his armor. Especially the mail on his arms, and the etchings on the chest plate.
If there was anything in it I could see a little off, it's in how the cape is draped over him. The top and parts immediately at his shoulders look great, but it looks a bit "starched" and stiff at the bottom. (and maybe a little short on the left too.) Not really sure what I could to help there. The only thing that pops to the top of me head would be to use a less "hard" a shade along the leading edge, and maybe throw in a sort of 'S' curve into it to show the cape is being blown. (I assume that's what you were going for.)