It all depends of course, on how closely you're following the concept art but if you're trying for a straight-up or near straight-up exact rendition, then what you're dealing with there is obvious a submarine, not a spaceship. The diffuse textures look good. :) pf
Hey that's looking great! But your right, it really do looks like its purely flat diffuse, no normals or spec at all. But speaking of which those black lines could do with some hilights & wear to define them as insets rather than just lines. But its looking really good so far, can't wait for more :)
Real easy way in udk to get that brass look, would be setting a shader up with lets say a vector param. This way you can control the over all color of your brass. Then I would mix in you're spec map from photoshop or where ever you made it from, multiply that by another vector param so you can get a tad bit more tweaking…