Being omniscient, you'd think God would remember if He was once a man and served under a different God on a different planet. Not so according to Mormonism, a religion famous for making the claim that "as man is, God once was. As God is, man may become." If you're a Christian, or even if you're not a Christian but are at least somewhat familiar with Christian doctrine, you'll already be able to see the problem with this. If you're a Mormon, I'd like you to follow the advice of your religion's second prophet, Brigham Young: "Take up the Bible, compare the religion of the Latter-Day Saints with it, and see if it will stand the test." (1)
If Brigham Young had taken his own advice, he'd see exactly what you're going to see now. The religion of the Latter-Day Saints will not stand the test of comparing it with the Bible. Rather, the Mormon belief that God was once not God, and that man can become a god, is pure blasphemy. Not only will man never become gods, no matter how deep into the Mormon religion they dive (Isaiah 43:10), but God personally declares that He does not know of any other gods. If He really had a god of His own, surely He'd remember that? In fact, since they allegedly reside in the same heaven, and created this world together (2), surely God would know of at least one other god if any existed?
Either God is a delusional god with the worst case of divine amnesia ever recorded, believing Himself to be the only one of His kind despite being in constant counsel with several others, one of which is His father, another His grandfather etc., or the Mormon religion is wrong. Not just wrong, but utterly blasphemous. According to the Bible, history, basic logic, and even the unwitting testimony of Joseph Smith and Brigham Young, the answer is the latter. The Latter-Day Saints are Latter-Day residents of Hell, unless they repent. The true Gospel will never allow you to become a god, but it will allow you to live with the one true God. This is an eternal fate that you certainly do not deserve, but one for which you were nevertheless designed. The blood of Jesus, spilled for every sin you have ever committed, has bought it for you. And here's the best part: It's not "after all we can do", but after all He has done. And so, my Mormon friends, I offer you a choice in the name of Jesus Christ: Work to earn godhood, inevitably failing and being condemned to Hell, forever separated from God, or accept the free gift of grace, for which all the work has been done already, and live with God for all eternity. To me, it's a no brainer. I'll leave it to you to decide whether or not you agree.
References
1. Young, Brigham - Journal of Discourses, vol. 16:46, 1873
2. Pearl of Great Price, Book of Abraham, Chapter 4, 1851