The author set this up exactly how the Namek saga of DBZ ended.
Goku has reached a new and unheard of height of power. After a long, grueling battle, his enemy can no longer defend himself and is begging for his life.
One can only hope Goku has noticed these parallels with his battle with Frieza and will make his next choice carefully. He's obviously in a clear state of mind, otherwise he wouldn't be able to hold that form.