Finish the game first, people.
At first, I thought the joke was along these lines: "sorry, but free will is a pretty useless thing to have if it doesn't work properly." ~Quote some reviewer below me who ironically didn't get the point of the game.
After finishing the level, when I got to the <SPOILER ALERT> setting William free thing, the small little revelation made me smile. If you don't get to free Will, you lose your free will! I thought it was a cute joke.
However, the joke could have been a little better if, after you rescue William, you are allowed to play the game again FREELY.
(P.S: I sure wish I thought of this idea in :the game:. Brilliant concept here: short but sweet.)