His stuff had a real honesty to them. Something recognizably industrial to them even though they exist in the fantastic. Hell, just a glance at his infographic decals posted above, you can pretty much figure what they mean by visuals alone.
I didn't realize who it was, though I recognized the name, until I saw the Hammerhead drawing he did for ANH. The Art of SW book had several of his alien sketches that I always really liked.