Walk softly...and carry a big gun!
ZOMG SPACE MARINES!
i cant recall how many hours i wasted painting my tabletop black templars squads, now they are gathering the dust on a bookshelf
pic is quite good, but the yellow marine lack a little bit of proportions, working on that could make your art better
the 3 other look fine, i would also totally redraw his chainsword, the way i look at it its like it have no handle and just a sawblade...
the blue one is my favorite, personally speaking, mostly because hes better proportionned than the 3 others and also have a very dynamic pose
i would recommend drawing shades, if you use photoshop and need pointers pm me i could teach you a few tricks , but needless to say that the internet is crumbling under bazillions of shade tutorials, or try Suzuran's tutorials here on NewGrounds, they are awesome