The bottom looks way too diagonal. More shading on the black, and even the visor if you want (since visors generally tend to reflect more light than the helmets). The lineart on the bottom of the visor doesnt match the top. The shading on the red stripe in the middle is bottom-up, which isn't generaly used in graal graphics. But it's your hat, your decision.

I think you've got a good start here, just a few things that could be looked at. Look forward to seeing the finished product.