Good work. You have a nice style. Your lines are smooth and crisp, and you have a knack for using texture and lines to create the illusion of depth and shadow. The foreshortening on the last image is rather impressive. The third image could use a little more definition, though. The form gets a little confusing toward the bottom before the black texture starts.
What sort of project are these for? If they're meant to be logos, prints, or something else of that sort, then they're fine. But if they're meant to be regular pictures, then they could use some work on the composition. They all feel as though they have a lot of empty space, which is fine for prints or logos but not so much for regular drawings.