For the shadows, they are CPU/GPU intensive. those actual simple blobs are really ok. What could be done would be make them less transparent and more noticeable like in some Iphone games.
@Joga: Great sculpt (yes sculptris rules) ! Your retopology seems very hight in terms of polygons for the low poly version ? will it be a giant fly or a big boss ? caus such level of details should be for camera very near and perhaps it won't be lot of times where the player will see it closer ? At some distance from camera, lot of polygons won't bring definition on your model, you can optimize. Anyway great model