My friend, this is very nice work, but there is this problem people have been mentioning with the hands. However, they just say "something" is wrong, but I have spotted what's bothering.
I went through all the trouble of making a Newgrounds account so I could share my insight, not to mock you, but rather so you may have feedback and not make the same mistake again:
While both elbows are located at the same distance, the right arm is visibly longer than the left. It's hardly visible, in fact I did not even notice it on my first view of your drawing. It's only when I read of it in the comments that I went back for a closer inspection and spotted it.
Hope this helps