In an interview with John Piper, Founder & Teacher, Desiring God, he actually lists several traits of a poor, easily-forgetable sermon.
"Well, I do want to say right off the bat, it is possible to be rigorously faithful to the wording, the logic, the purpose of the biblical text and be engaging and not too technical. It is possible. If somebody told me, “Piper, your messages are too technical and they’re not engaging,” I would not blow it off. I would take that criticism seriously. I would make every effort to be both: engaging and rigorously devoted to the wording of the text."
You can read the whole interview HERE. Briefly, his list is as follows:
1. Lacking Clarity
2. Too Abstract
3. Irrelevant to Real Life
4. Emotionally Distant
5. Not Interesting
6. Too Technical
He concludes saying we all ought to strive to be both rigorous and engaging. Amen.