I got a tip for you =O
When applying your brushes, make sure that it err... flows with the render.
For example, your first pikachu sig is nice because the brushes flow with the render(pikachu).
For your second sig, the spots are just "static". They just don't carry any flow, and thus making it less appealing.
*I hope I'm making sense x.x*
Anyways, the more you practice, the better you'll get.
Here's a toast to your success.