Wow Chow, it's always a pleasure to see your new updates You inspire me to do studies like this. I know you say to critique, but.. I can't really see anything wrong in terms of values and anatomy. I guess the only thing might be that you might want to paint animals too, since those are anatomical/technical studies as well and will help build your library for future monsters
oh, and come join the spartan gestures and daily sketch group sometime!