In a study of 200 ad competition winners and finalists, 89% could be classified into six basic templates. You would expect that highly creative ads be greatly varied, however a great majority fit into just a few categories. The categories were: Pictorial analogy, Extreme Consequences, Extreme Situations, Competition (product is shown winning against another product), Interactive Experiments (audience can test the claim themselves) and Dimensionality Alteration (like a time alteration). They also tested 200 other ads that did not win awards and only 2% could be classified. All good ads are similar, while bad ads are bad for different reasons.
From Made to Stick and the study "The Fundamental Templates of Quality Ads" by Goldenberg, Mazursky, and Solomon in 1999.