Along with what's already been said, your diffuse is pretty bright for something metal. When texturing metal you generally want a darker diffuse with high spec letting the interaction of the two created the final colors rather than the diffuse doing all the work.
Pardon the ignorance, but what do they mean by "5 materials"? Like a diffuse/specular/normal/gloss? Do they mean materials presented, like you're supposed to make the model somehow incorporate elements of plastic and metal to test you're surface texturing?
Hmm. Yeah, seen this test before. My first reaction is that the surface quality of your object is being almost entirely determined by the diffuse and the other maps aren't quite getting to show off as well. Some ideas 1. Bake a projected ao map from your high poly and a simple ao map from the combined low poly, then…
I noticed on the 2nd image that the 'CRS-384' signage on the right side is flipped. Looking at your diffuse I think you can definitely push more on texturing, stuff like adding in smaller frequency details like bolts/screws to define the panels a bit better. Most of your metal are the same tone, the large 'A' frame could…