Colours aside, the whole concept of a Pokeball head has been use quite a lot, but as you're doing this for fun, I'll comment on the execution.
If you look at a normal Pokeball as a reference, the front of the Pokeball is similar to two circles with bevel, or cel shaded (which you've done a bit of in your texture)
As you've done this by a brush (You can tell by the strokes and as you're intending to get an anime/cartoon like style I would suggest using the pen tool (Photoshop) or the Path tool (GIMP) to improve over your brush use.
The fact that you haven't mirrored isn't the best idea for this texture, as Pokeballs are basically symmetric, I would suggest copying a part of the side to the back to remove the seam (The hole at the back).
The asymmetric shadow thing on the front looks quite nice for your level (Based on what techniques you don't know etc), but you could refine it a bit more by adding a few more shades in.
Now that that's done with, I would suggest looking at the shape of the front, the ring in the middle is too small and doesn't look that nice.
Oh, and there is an odd dot in the middle.
Overall/tl;dr:
I would suggest keeping the level of simplicity, keep the asymmetric shadows and details, but mirror the base of the texture (For this kind of thing anyway)
Use pentool/pathtool for the style you're intending to get and look at a reference for this kind of thing.
Feel free to PM me if you want me to explain this better, because I am quite awful at doing so :c
And/Or feel free to PM me if you want terrible advice (I'm not exactly very good with art)/ me to show you anything you want.
Keep doing this kind of thing and you'll get the hang of doing textures and how they map around spheres/any other object you want to map them round.
Once and if you get more into texturing, I will give you more specific criticism on how to improve on this texture (Where it's good to highlight/shade and what styles suit it and mapping.)
Last edited by notnoob; Sep 1, 2012 at 08:24 PM.
Reason: MORE EDITING