In this image you can see that when you build a level out of many sprites, the shadowcasting looks all messed up. Either the light can reach an area or it can't. Shadows of diferent opacity should only be used when ther's multiple light sources.
In this image where ther's just one shadow caster it looks just like it should:
But when you ad two objects it doesn't look right.
This is what it should look like.
As you can see the shadow caster engine doesn't render the shadows the right way. It shouldn't make the shadow darker if there are two objects blocking the light. It should make all shadows have the same color, but make it brighter if there a lightsource reaching it.