Nice
Generally, mouse-avoidance and maze games irritate me -- I've never had a mouse go PRECICELY where I was moving it to. Be they ball or optical, things go wrong and they stick and/or jump. Bearing that in mind, your collision detection appears to be forgiving -- not triggering until the whole dot goes over the line.
It looks nice. The 'START' and 'END' buttons are nicely textured, and the maze walls aren't bland. As far as maze difficulty, you'll have to talk to someone else. My mouse apparently needs cleaning again. :(