Is Islam the only religion acceptable to the Creator?

Yes! As explained in the introduction, Islam means peace through the submission to the Will of Allaah. One who does this is called a Muslim. Therefore, the only thing acceptable to the Creator is submission to Him. Allaah says: "Do they seek other than the Religion of Allaah (Islam)? While to Him submit all other creatures in the heavens and the Earth, willingly or unwillingly. And to Him they shall all be returned. Say, ‘We believe in Allaah and what was sent down to us, and what was sent down to Abraham, Ismail, Isaac, Jacob and the tribes, and what was revealed to Moses, Jesus, and the Prophets from their Lord. We make no distinction between them, and to Him (Allaah) we have submitted (in Islam)."And whosoever seeks a religion other than Islam, it will never be accepted of him, and in the hereafter he will be of the losers (in the hellfire)." (Qur’an 3:83-85)