At present, the white/grey outline doesn't add anything to this piece. I get what you're trying to do but I think it would look more effective if you started whith the lighter colour closest to the snail and then AA the the second line, as at the moment it looks too jaggy against the black background. As for the snail it appears to be pillow shaded. Pick a light source (ie. top right hand corner) and then shade it respectively and it should look alot better :)
i edit image ,now is in Dark Forest :D