Add more shading. It is indeed freehand and that's good, but on the other hand those green stuff don't really look like rays. Rays have a white part as well, and well... more depth. Have a look at these examples:
http://www.wc3sear.ch/?p=Icons&ID=9891
http://www.wc3sear.ch/?p=Icons&ID=4668
http://www.wc3sear.ch/?p=Icons&ID=5399
~Daelin