I wish you could give a little moer definition to the zippo to give it some depth, like the heart, but you're at your color limit so there's not too much to do. The size is good, the image is fantastic! Wonder Twins power activate!
Yeah, I agree with all the people commenting on the 16 bit look, it looks real ace. The colour limit might turn out to be your friend with this one, maybe use some of that darker shade of grey to give the zippo that depth it needs?