This is an excerpt from a letter Richard Feynman wrote in March 1958, back when I was just about exactly one year old and still wearing diapers. He'd been doing some consulting work for the entertainment industry, and wasn't very happy with their attitude.
The idea that movie people know how to present this stuff, because they are entertainment-wise and the scientists aren't is wrong. They have no experience in explaining ideas, witness all movies, and I do. I am a successful lecturer in physics for popular audiences. The real entertainment gimmick is the excitement, drama and mystery of the subject matter. People love to learn something, they are "entertained" enormously by being allowed to understand a little bit of something they never understood before. One must have faith in the subject and in people's interest in it. Otherwise just use a Western to sell telephones! The faith in the value of the subject matter must be sincere and show through clearly. All gimmicks, etc. should be subservient to this. They should help in explaining and describing the subject, and not in entertaining. Entertainment will be an automatic byproduct.
I don't entirely agree with him — most entertainment isn't at all didactic — but he's right that when you are trying to get an informative message across, the gimmicks have to be the garnish, not the main course, and the work you do in developing the medium has to focus on making the message itself interesting.
For instance, the Book of Kells is an artistic wonder, an illuminated manuscript that anyone could spend hours and days staring at, enjoying the script and the little illustrations all over the pages. But those are geegaws that don't make the content clearer or more palatable — they allow one to appreciate it while ignoring the message (and a good thing, too — it's just the dull old gospels turned into art). In communicating science, the goal is not to load it up with bells and whistles, but to make the story you're telling clear and accessible. You don't want the listener or reader to overlook the message.
Although I have seen a few evil PowerPoint presentations that show the creator doesn't understand that concept…