First, welcome to Pixelation!
Second off, there are some problems I'd like to point out:
Flat shading. Just adding a rim of light along the outlines you've drawn isn't how lighting works. This leads to inconsistency in the direction of the light-source. Recognize the forms your drawing is made out of, and try shading around that. The sprite is in need of stronger shadows as well, or overall more contrast.
Which is what I've done in this edit:

Eyes don't glow in the dark. There are instances when their whites are visible of course, but they're not usually this white. Got rid of the stark white color, and used that for another color. I didn't do much for the guy on the right though.
Minor anatomy/proportion tweaking of the neck and shoulder muscles as well. There's some lineart for clearer reference on the guy to the left.