I see what you mean with the legs, they could definitely be less flat.
As with the helmet, I already did take reflection into account, the moon is grey and the sky is black so it's not the most obvious detail.
In my normal drawings, I've always struggled to let myself give things contrast for some reason, I guess mentally I don't want things to go from one color to another too quickly despite the fact that doing so looks better, and I think I've done a similar thing here, not giving it enough contrast.
That said, here are some quick changes I made with all that in mind:

