I don't have a problem with any of the positions or proportions you employed. In fact, this is very good. The only thing it lacks is fluid animation, which you can probably fix with 2 or 3 more frames.
It made me laugh...Like it's a bit uncoordinated. Those muscles look freaky too...O_o Maybe study human anatomy and focus on the design before you animate?
Needs to be a lot more smoother.
Can't really see what's going on there when it swings it's arms :/
Wow this loks awesome :O but I agree the animation just doesn't look smooth enough