I have never had an oral exam, but I have always thought it would be great for smaller classes. Basically I would love to have an exam where I sit down with a professor for 30 minutes to an hour and talk about the content and answer questions they ask. I feel like it would be a bit more in-depth while also eliminating the possibility of misunderstanding a mistakenly ambiguous question. I am not sure how realistic that is for a class above about 15 students, and also how things like disabilities would be handled, but I'd love to try it.