This animation was awesome (And I applaud your patience), but I think this animation could be far more visually appealing if you used some nicer colors. Maybe subtly different lineart colors on the 2 characters also. Another thing would be putting more effort into your backgrounds (and not using flash gradients), and also changing the colors a bit. Less harsh colors can be a lot easier on the eyes, and when used correctly together can have a momentous effect on your animation.