I guess it depends on what he's supposed to be doing. But right now, it looks like he just tripped and is falling.
I'd suggest looking at some pictures of actual runners. Very rarely is there any significant declination, except in those first strides as they launch from the starting position (a 3 or 4 point stance which Marines would rarely find themselves in, especially carrying a bolter). That's something I can only think has been invented by comic book artists, lol.
And the angles of your pictures make it difficult to see much of the model, at least from a useful perspective for feedback.
I agree True scales look great but this guy is leaning over a little bit to much makes him look unbalanced I would suggest to tilt him back slightly and maybe even close the distance between his legs I'm not sure even a spacemarine can fire accurately at full sprint also check out Sprugly's post he has done some true scale Chaos marines http://www.warseer.com/forums/showth...y-s-blog/page2 . Good work so far.
See one melée of unruly Orks and you've seen a maul
Finally going to paint a whole army... maybehttp://www.warseer.com/forums/showthread.php?t=295015