I thought it was really clever how you could use Bind to pull Null's arms out and expose the weak points.
Also, Null's design is pretty neat, though very basic-- but I think that's because of the art style of the game as a whole. If it had the art style of, oh, say, Twilight Princess, then... Null might have been the most potent nightmare fuel this series has ever seen. (It still kind of is, at least psychologically, when you consider that it's the literal embodiment of the chaos that existed before the world was created. The formless nothingness, given form and substance.)