I like it. Attached thumbnail picture reminds me of a Marcus Phoenix from Gears Of War, because of hard and sharp lines, massive forhead muscles, wide and big nose, and a lot of wrinkles .
In order to make my post constructive, without any harm meant, I'd like to comment on few things. I'd say, it depends on what you're aiming at; is it acurate anatomy sculpting, or just, let's call it, free form. When someone's sculpting human head (or any other part), with good, or great shaders and textures applied, it turns out, that many people expect acurate human anatomy as well.
But, just to make few comments on what I think should be a little bit changed if it's about acurate human anatomy (looking at thumbnail picture). Nose bridge is somehow thin at the top, and below it there is a sharp, and wide line. It looks like bones grew that way. Forehead muscles, right above nose bridge, are separated with indentions. There's a little bit too much wrinkles beneath the eyes, and they are a little bit too close to the lower eyelid.
I hope you found something valuable in my post,