i guess the essential difference is that neoclassicals view the economy as flexible and self-adjusting, needing little or no government intervention. also, emphasis on rational expectations and inflation being a monetary phenomenon. keynesians on other hand dispute notions of flexibility and emphasise the importance of government intervention in the economy.
i think atta said the as/ad curve was formed by neoclassical theorists who wanted to show the keynesian ad curve is compatible with their own theories, that was either in lecture 9/lecture 10, can't remember. but i don't think that's a very significant difference between the two.