Your series does not speak for itself. If you had not told about your exercise, your examples could mean anything. The concept is bad. Your posters are not reduced to essentials, but simply boring. The exercise seems to be a typical ‘art-teacher-exercise’, which is not your fault.

I'm not altogether sure what you're actual brief was, but I think you may want to start off by looking at the meaning of all three words. Simple, explicit and diffusive mean very different things. Perhaps try designing a poster where you represent the meaning of each word. What would a 'simple' poster look like, or an 'explicit' poster? etc etc

Unless I've completely misunderstood what you're trying to do, in which case disregard the above.