the .jpg is killing your colors. When zoomed, the sprite at actual size looks very different from the zoomed one below it.
I quickly re-pixeled it over yours (colors are probably wrong / different, so post your original as gif or png so others can edit properly) and did an edit.
Removed the dithering and altered the shading here and there. I'm really new to pixel art, so others will probably have better edits.
One thing, tho: if you're dithering for texture then that's cool, but if you're trying to make the dark grey in your pallet appear a little lighter, you'd be better off just choosing a lighter shade. Unless you're stuck with that shade due to limitations or something. i didn't change it, myself.
Also, the red in the right robot and the blue in this one are hard to notice unless it's zoomed in on. Even in the png version here. You might want to make those brighter or give them a glow or somehow make them contrast more with their surrounding shades to make the eyes and little color areas stick out a wee bit more.
