This is looking much better. I think the next thing you should work on is a more defined light source; at the moment, it appears like there is two white lights on each side of the monster, and I don't think that's what you're going for. Instead, try a single light source--picking a corner usually works pretty well, as made example by Tremulant's choice to light from the top left corner in his edit. Alternately, you could place the light source directly above the alien for the easiest fix.
You say you might work on the colors soon, which is probably a good idea; the current colors aren't redundant, which is a good thing, but they also aren't very interesting. Probably playing with hue shifts would be your best bet to add to the interest.
Good luck, and keep pixelling!