Def needs more different colored parts. The elbow disc/joint could be a different color. Knee pads maybe. Gray discs on the chest (the gray ones) could change the base to be a different color as well.
Total retexture, chamfer the edges on shoulders and probably all over. Increase the luminance on that belt fed gun. Give it more prominence on its face, some asymmetry in its paintwork.
Get some ideas from his police droids on here http://skul4aface.blogspot.co.uk/
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http://fc09.deviantart.net/fs70/f/2010/131/c/b/Marine_Poses_by_SgtHK.jpg
Get some ideas from his police droids on here http://skul4aface.blogspot.co.uk/