It's looking awesome!
My one point about the visual style would be the lack of environment light/shadow on the hand-weapon and the lack of self-light/shadows on the hand weapon.

The environment is lit but the hand weapon doesn't change near or far from a light source. Edit-(I do not mean that the environment doesn't flat shade the whole sprite, I mean that the sprite color set doesn't change shading to faux it's shape.) -end edit. More to this is when the gun fires, shouldn't the hand-weapon receive lighting-shadowing colors and shifts for the gun blast light source?

Anyway, it looks great and I've no experience with 8-bit shooters so my points might just be out of place.