Off-topic:
Well, I must say that in my opinion, Starcraft 2's gameplay demo looks sleeker than any pixel art game I'll ever find. It's just that I don't think you can get that level of dynamicism and perfection when you're using pixels at low resolutions.
On-topic:
First of all, I strongly suggest you remove the pink background, until the final version of your Firebat. Reason? I find it extremely painful to work for hours on a piece that has the brightest, most annoying possible pink as a background. You'll work better with another background - you can either make it plain white, or pick the average color your background will have, to make sure your sprite will look good when it's superposed to the real background.
I think you should rework the pose of the legs. At the moment, your Firebat would probably fall backwards from the weight of his jet-pack, or whatever it is. His stiff appearance is probably on the most part because of the legs.
You also made the shading too monotonous in many areas. It's a common mistake to do, when you're starting off art. One tries to make the shading equal on all parts of the pece, in an attempt to make everything look like it fits together. You're also pillow shading on the chest plate, which is bad. Pillow shading is the act of shading a piece from the outline to the center, darkest near the outline, brightest at the center.
It's good that you didn't use too many colors, but I think you should rethink your palette. Chromatic palettes (palettes that don't have any saturation or hue shift between shades) make a piece very boring. Many artists make their shadow shades a slightly bluish hue, whereas their light shades a slightly yellowish hue. This makes the piece more interesting to look at.
In this case, I suggest making your dark shades slightly purple, and your highlights slightly orange. You can keep the white, since the Firebat seems to be wearing very shiny armor.
Last thing: the boots aren't in complete shadow - I would shade them a bit just to give the viewer an idea of their form.
Hope it helps.
.ceddo