I thought the colors looked kind of drab, I made a pallete edit. I probably over-saturated them abit, but it gives them more pop.
also correct me if I'm wrong, but wasn't galaga on a black background, with the enemies facing downwards? It doesn't really matter much, but I think its better to design sprites in positions/backgrounds relevant to them.
there is also the issue of the weird shading, and head positions, but I haven't really touched on that so meh.