I would suggest giving him a slightly more dinosaurish legs, lengthen the bones in the foot to about half-way up his lower leg, so it looks like two knees. It's pretty cliche for dragons, but that's probably because it usually looks better. Also, I think the legs need to be pushed backwards, it looks like is feet are up close to us, and his body falling over backwards.
The shading could also use some work, right now you have just pillowshaded the muscle groups. The thing is that you're thinking in shapes, rather than light and shadow. Picture how the light will flow over the bulges in the muscle: the upper arms will be pretty evenly lit, use mainly your lightest color(s), and shade with only the midtones. In the areas that'll be in shadow, you can pretty much flatten it out with your darker tones, it'll seem like you're losing detail, but the 3D look will make up for it.
I think the arm's anatomy was pretty much spot-on in the original sketch, but in the latest iteration it almost doesn't resemble a normal arm at all.
Don't let my post bring your down though. Great work so far, I do like the texture for the skin you've got, and you did a great job on the face! Take it a bit further and it'll be excellent.