The combine sniper looks great. His posture looks almost machine like; he sits and waits, letting his supernatural eyes scan the horizon as his biomodified flinger slowly caress the trigger.
The legs are very sketchy in comparison to the head and gun, which is a shame, as the detail you've put into the helmet especially is astonishing. I love all your other work too, especially the citadel
I think the sketchy painting of the legs kind've makes you focus more on the head and gives an idea that he is all focused in his brain... well, maybe not that, but I think that the blurred effect they give could somehow contribute to it...