Actually, I think it might be more the torso and some of the shapes at fault here. I did a revision, it's a gif so you can see what I changed easier.

 I did some edits to the face too, to give the eyes a more natural shape and throw in some of the usual topography (our eyes usually cast a shadow between them and the bridge of the nose, for example), in addition to changing that bit of muscle that goes around the back of our neck between our shoulders, good instinct having that in there it just needed to go left a bit!
I also rounded out the breasts some and pulled the torso out to the left.

And here's an edit I did in addition to bollie's, I kept colors the same but tweaked the shading and some of the shapes to give him a more visible pose and a bit of depth.
Notably, I made the shading on that spiky anime hair a bit more uneven, to imply additional spikes facing the camera and better define the shapes on the right.
I also tweaked the shield to be at a more natural angle, most of the time shields are held at a slight angle unless they're held up Spartan-style right in front of the face (at least from what I've seen in movies), so I made it pitch at an angle. This made him look like he was taking a step forward/back, so I also changed his legs to give him a more guarded, sideways stance.
Fun fact: I actually took a bit of martial arts, and one of the basic things I remember from that long-ago time was that they do that sideways stance to reduce how much of you is available to the assailant to hit!
So, the more sideways a person is to the camera, the more a trained they'll look.

Ooh, neat. I'll have to remember that dot-matrix look, that'd be handy for environment stuff.

I'd say the breathing is too exaggerated, it makes it look more like a surprised gasp. To allieviate this I just removed the top frame, lowered the left-most arm to not jump up as much, and did some mild tweaks to the left leg to give it less shrinky-shins and a foot.