You can differentiate good presentations from bad one looking at the slides and listening to the speaker.
If the slides are filled with too much information, and the speaker is trying to stuff as much content as possible, in most of the cases it will be a BAD presentation.
People could think that they learned a lot of things, but at the end they will retain very few information.
Define the value you want to leave to your audience, and craft your presentation in a way that the value is maximized, and that you don’t spend too much time on insignificant details.
Less is more, when it’s valuable!