How to improve team's learning presentations

Hi

We have internal presentation where people will present what they're working on, or new technology that people know. Its a great idea, but the quality has been really bad. People doing demos where no one is following, pages and pages of notes which are difficult to understand, either too simple or too complicated. Usually they go way too long.

Usually everyone politely says thanks that's useful, but usually no one is learning anything.

Has anyone done similar and got useful content? or even found a way to produce positive feedback.