Let's see...
The poses are very stiff, using a lot of straight angles.
The proportion is extremely off, and I don't mean their heads are too big or anything: that's clearly intentional and has been pulled off well many times before. Examples: I mean the torso is rather short in comparison to the legs, the right arm seems longer than the left, the left leg seems longer than the right, the knees are bent awkwardly, the head is shaped awkwardly, and what's up with those hands? I recommend a basic understanding of anatomy, and not down to every muscle unless one of them is going to be particularly muscular, just an overall idea of what the human body looks like, so you don't end up with noodle-limbs like these.
Why only one eye on some sprites?
The sprites that are "shaded" are mostly just "pillow-shaded", meaning there's no actual light source--instead you just pick increasingly lighter colors from the outline in. That's a definite no-no.
I'll whip up a quick edit pretty soon.