A good concept, and polishing up the graphics would make it 3 times better. Adding in a easier/faster method to lay tracks would make it 3 times better, and some cool sound/music would help too.
I think the collision checking may be a little sketchy. Sometimes I can move my mouse really fast to get through stuff, other times I think I hit pieces, but I don't dim.
Instead of having to click the ball, you should only need the circle to be touching it when you click. I see some potential here. It was actually pretty fun for some reason.