Man you render work is crazy awesome! I also really like the design of your helmet and seeing the left over constructive lines I can see you are really adept at laying down forms . There is one thing I've noticed though though after seeing all your drawings and it is that I feel that your faces seem pretty similar between some of your characters.
Thanks! Without any particular intention, which is what a sketch like this is, one tends to revert to one's defaults. I'm currently working on a public commission with a couple dozen portraits, I get plenty of practice.