The human sprite looks very good as far as form, coloring, etc. goes. The walking animation from the front is a marked improvement. The back view animation lacks... "umph". The back itself needs more movement, and while flipping the front walking animation is a good start, the legs need to be tweaked more--as of now, it kind of looks like the character's legs are on backwards.
As far as your aquatic race, you are certainly moving in the right direction. From what you've said previously, too much realism would ruin what you're going for, so it's a matter of striking that balance.
Keep up the good work!