It's looking fantastic! Great work on the detail.
I would agree with the others that the lower arms look a little big, but only in proportion to/when compared with, the upper arms. The way to solve that would be to make the upper arms bigger to match the lower arms.
That way you don't have to worry about scaling down the lower arms and it would serve to make you look more bulky/muscular.
I hope that makes sense.
Keep up the good work.