im not so good at giving critique on art but i'll try it out anyway
http://i.imgur.com/fi8RHwg.jpg <- redlines are my suggestions, greenlines are yours
first thing i noticed was that medic's eyes look off-centered, so what i'd do is shift his nose and his right eye over so it does look more in the middle.
another thing is that your ears and your nose tend to line up perpendicular to each other, and the medic's ear was hitched up a little far, making his jaw look a bit larger than it should. (looking back on it now, my redlines are a little sloppy, the line at the top of the ear/nose should be higher up.)
but i dunno if it's just stylistic choice, since i prefer to draw kind of skinnier and longer necks, but it feels like the medic's is too short and muscular for his type of build.
yeah
sorry im bad at this kinda stuff. :(