Ok first of all you need to incorperate easing into your animations, easing is the acceleration and the deceleration of a movement, sort of like this...
l-l--l---l----------l---l--l-l
Allthough I think you allready know this, but you aren't really incorperating it into your animations, the best way I've found of practising is doing an animation of a ball taking off and easing to a stop.
Secondly you should work on stiffness, your animations are extremely stiff, remember, you should move EVERY joint in EVERY frame in order to stop it entirely, however, whilst doing this I can garantee that you'll run into another problem which is shakyness.
Basicly, you'll fight shakyness with easing, so say you where moving an arm, to stop it being shaky it would have to ease to start with, then followthrough without any noticible jerks or wierd movements, and ease to a stop. This is called [B]flow[B]
And finally you need to work on physics, however this is extremely complicated and I don't want to destroy your mind with complicated things, so I'll skip that bit.
Anyway, after you've mastered all that you should be at least a high amateur, if not bordering on pro.