[anigbrowl]

No, but they definitely help. My rule on this is that slides should make it easier to follow a talk and get back on track if your attention wanders. If the slides require extensive explanation then the information is probably better summarized in the talk and laid out in greater detail in a paper.

Obviously a lot depends on your audience. Slides at an academic symposium can be dense enough that you can get the gist of the talk from just looking at the slide deck, slides for an introductory talk on a subject should be more like the list of contents in a book.