Hi man ! Well, from what i've seen there are some good points here ! there is just a few things that i wanna talk about . On your last faces studies, i think you're nothing thinking enough about the perspective ! and this is the same in some parts of your characters ! i guess until you have solid constructions and proportions on your characters, i find that it's not interesting to render them on photoshop ! you can only work with line until you have a decent understanding of human being and of armors, etc, and you can still practice rendering through studies ! third, i find that your values doesn't describe well the forms you're painting ! but it's not only a matter of values, it's also about edges ! so i suggest you to study only in b&w for about 2 months, and then come back with colors too, because it seems you can pick up the right colors, but have hard times with values ^^
Here is what i had to say,you can take it or leave it ^^
But anyway,i think you're on the right path ! keep it up !