This is a piece I'm working on for a friend. I definately could use some critique on well... everything. Some background ideas would be much appreciated as well...
The head looks a bit on the small side, with the face squashed into the lower third. The fabric of his tabard doesn't really have any shape (ripples etc) and the cross doesn't follow it, it just looks flat. The perespective doesn't work on the hammer thing he's holding. (at first I thought it was a fat hand gun). The anatomy is off in several other ways. He seems to be walking like a robot too. I'm still slightly unsure wheter he's supposed to be a medieval or futuristic warrior. If it's the former it might be helpful for you to find some references for suits of armour. Also you want to work out the lighting. If there is a strong overhead light to cast those dark shadows under his brow and nose, then the same light should create just as strong shadows on various parts of his body.
maybe the head is a little too small? dunno..
I love his outfit, and the mood can be felt quite well. What he's holding is not quite obvious. maybe you should work more on that part. I'd suggest you make a dark background, anyways, don't let it gray!!
for the hammer at the angle the heads at, the handle would go almost directly back, for the legs it looks like he is walking but his upper body isn't reacting at all to the motion, also I would move the figure slightly away from the right edge as it it creating awkward tension between the arm and edge. the piece certainly has potential though once you fix some of the issues. nice job