Unique User Control
Many people have already said that the artwork used here is amazing. What I also want to mention is that I find it very interesting that the user is able to make choices about what each picture should look like. If you'll notice, whenever you click on a spot, it changes to match the opposite picture. Therefore, if you click on the versions of the spots which you don't like, they will all change to make the perfect picture. I just thought it seemed really cool to sort of have a part in creating this wonderful artwork!