Gotta hand it to ya, you're a pretty impressive graphic artist. While we may not always be 100% in agreement on the technical/engineering-type stuff, I can honestly say that you beat me handily in this area! You ought to be working in comics... your ability to capture the general appearance of people is definitely on par with most of the folks working in that field, Alex Ross notwithstanding! I have to admit that your Troi doesn't look much like I see Marina Sirtis, though recognizable when you know the context. But your Tuvok and Riker are perfectly recognizable.
Out of curiousity... what software are you using? (Or is this old-fashioned board work?) I've played around with a couple of things, but I bought the CorelDraw suite a while back and so I'm pretty much committed to using that. Problem is, while I'm damned good at the machine design side (enough to make a very good living doing just that), I can't seem to come up with good graphics (like a ship or a class logo). Just not my forte..