Your use of lines in this piece is done very well but if you want to improve I can make a suggestion. You can play around with the thickness and thinness of the lines. It can be played around in many ways, lines that are thicker can mean that something is more important, it could mean that it is closer or even far away (it depends on the artist's vision...it's sort of an optical illusion thing)....lines that are thinner are either less important, further away or up close (that depends on the artist's vision). I believe that although you drawing are pretty good now, they can have much more umph.

You can look at this artist and his line art before he paints it in and you'll see how he uses the different strengths in line
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I believe a good way to improve is by observing what other artists do

First of all, I really like the character design and the varying poses of the arms. The lines are awesomely smooth and clean too but maybe you should vary the thickness in them a little? His torso also seems a little long but that could also be a part of your style (which is really cool by the way).

Otherwise, I think this is neat as it is.

P.S I've got to say I really dig the design on the guns! I'd love to see this guy colored as he'd make a really awesome comic book character; a crazy mad scientist!