His enthusiastic teaching style is unparalleled. His ability to turn a phrase is also highly appreciated.
Nothing at all.
Carl was excellent at explaining everything in a calm and measured manner. Always answered questions and threw various comedic moments into a lecture to stop it becoming an hour of him talking. Informative, the level of knowledge is beyond understanding for me. Doing whole lectures off the top of his head when he would lose pointers for the lecture. Best lecturer ever.
Nothing at all, a perfect specimen could not exist in academia and the world will be poorer for his leaving.