There's two main things I think about when responding to the "What makes Great Preaching?" question.
First is of course the spiritual health and strength of the preacher. The Word of God is powerful but our lives are often the greatest hinderance to word going out. Before worrying about preaching great messages, we must consider the strength of our mind, body, and soul. I love how my pastor, Jurgen Matthesius, says, "Don't practice what you preach, PREACH what you practice."
The other thing that comes to mind of what makes great preaching is transformation in your audience. At the end of the day, it doesn't matter how smart or eloquent you sound, if you're not helping people encounter the power and truth of God's word in a way that their lives are transformed, then you're just giving a TEDtalk. I've heard it said, "Preach to their Monday." Which is great, or preach to their eternity would be another great statement.
Let's not just give talks, let's impart and boldly preach the truth in a way that wakes them up and stirs them up!
For more on preaching check out the "Preaching With Authority Book" or the online course.