Modelling looks good. But I think the main issue is that you have way to much information in your diffuse. Metal is defined by the spec/reflect/glossiness and putting too much info into your diffuse takes away from those.
I think the modeling is solid, but the materials are lacking. The biggest problem IMO is that it looks like it's all made of the same material. I think you should make the painted parts less glossy and more diffuse to separate it further from the other parts. On the concept it also looks like there's both black painted…