First let's look at the Mormon view of creation, to see how their gods fit into the larger pattern of created beings. A person like you or me (or even plants and animals) was once a spirit being created by Heavenly Father, dwelling with him in Heaven, unable to be harmed or die, but also not yet living in a physical body.
At some point, this spirit is born on our world in a physical body, subject to pain, decay, and death. When we die, the spirit separates from the body and returns to the spirit world, generally back to Heaven to re-join Heavenly Father if the person lived a righteous life.
Eventually, these post-mortal spirit beings will undergo a bodily resurrection, only now this eternal body will not be subject to pain, sinfulness, death, and so on. Depending on how righteously they lived as mortals, these resurrected bodies will occupy higher or lower levels of heavenly bliss. If they make it to the highest level, they will become gods themselves like their Heavenly Father, and thereby become capable of ruling over a world of their own, creating a population of spirit beings that will be born on their world, and receiving the worship of the mortals on their world.
Mormonism had been fairly clear about human beings who reached the highest level of Heaven becoming gods in this sense -- creator gods who would then oversee their own world. As it has sought more mainstream acceptance over the past 30 years, the idea has been downplayed but not denied. It is now framed as something that is possible, that we may speculate about and even hope for, but not necessarily something we can be totally certain about -- or at least not in front of the non-Mormon majority, who might find the whole idea a bit out-there.
The state of eternally residing with our Heavenly Father in bodily form -- both him and us -- is called "exaltation," and is the last stage of the "eternal progression" that began when we were pre-mortal spirits. A being in that state is called "exalted".
You may be thinking that a return to our creator for eternity may not sound too different from the Christian view of the afterlife. But here's what makes Mormonism unique: it holds that our Heavenly Father has gone through the eternal progression himself. He began as a pre-mortal spirit, lived as a righteous mortal, was resurrected in flesh and bone, and attained the highest level of Heaven. In that most exalted state, he created all the spirits that will ever be born on our world.
Heavenly Father in Mormonism is not a figurative role model but a literal one -- if he made it, we could too. Or in the pithy phrasing of Lorenzo Snow, who would rise to Church President at the turn of the 20th century:
As man now is, God once was:
As God now is, man may be.
In Mormon theology, Heavenly Father, his spirit children, and the mortal beings they become, are all of the same genus, only at different stages along the eternal progression. But there is no unbridgeable metaphysical chasm between mankind and its creator. Indeed, we are caterpillars, and he is the butterfly.
Just as in the case of the looking forward idea -- can human beings become gods to populate a spirit world of their own? -- the backward-looking idea -- is Heavenly Father an exalted man who was once mortal like us? -- was clearly portrayed through most of LDS history. With the recent attempt to boost its mainstream appeal, this idea is being downplayed but not denied. I conclude that the view is still mainstream within their theology, given how common the view has always been, up to the highest levels of Church office, and how today's leaders are not clarifying by saying "No, those earlier prophets were off the mark, and Heavenly Father did not go through his own eternal progression."
All right, but how does that merit a term like "pagan"? Well, call it whatever you want, but that is a crucial part of pagan mythology -- gods are created, or perhaps emerge from the cosmic background, so that there was a time when they did not exist, or at least when they did not exist as gods. They may in fact stop being gods, if their god-like status is stripped away from them by another god, or if they switch from divine to mortal form in order to interact with human beings, when they would be susceptible to bodily harm.
Unlike pagan gods, whose divine vs. mortal status was subject to flux, mankind's creator god in Mormonism cannot have his divinity stripped away, or assume mortal nature after becoming a god. The eternal progression only flows one way.
Nevertheless, the fact remains that Heavenly Father has not existed as an entity forever back into the past, let alone as a divine entity. In fact, he is of the same genus as mankind, only at a more advanced stage along the eternal progression, having reached the highest degree of exaltation.
This central feature of Mormon theology marks it as though it had come from an earlier stage in the evolution of religion than those of the Axial Age and its off-shoots, including Second Temple Israelite religion, Christianity, Islam, Zoroastrianism, Buddhism, Taoism, and Greek Golden Age philosophy.
That shift circa 500 BC, give or take a few centuries on either side, forever did away with the notion of gods as created beings who looked and behaved anthropomorphically. The pantheon was whittled down to at most two creator gods (Zoroastrianism), usually one (the Abrahamic religions, Xenophanes, Aristotle's Unmoved Mover), but perhaps no god at all but an impersonal guiding force (Buddhism, Taoism). And importantly, these creator gods were not themselves created or emergent from a primordial cosmic stew. They were creators at the very dawn of time, and have always been transcendent.
Add to this departure regarding Heavenly Father, the view that human beings may become their own creator gods of other worlds, and you have an even further deviation from the Axial Age tradition. No matter how the nature of God was perceived during that time, it was certainly not possible for a mortal man to become such a god, or for God to have existed in mortal form before attaining godhood. The religious revolution of the mid-1st millennium BC separated God and mankind into two states of nature that were impossible to cross between.
In 19th-century America, Mormonism restored the much earlier pagan view of our creator as just one example of a created being, one who had existed in earlier mortal form, and whose godlike nature it was possible for us mortals to attain. This view continued to be mainstream among LDS Church leaders right through their fastest period of recent growth, roughly 1960 to 1990. Only since then has it been toned down, without disappearing or being denied, let alone denounced as a heresy.
This post has only touched on one aspect of God's nature in Mormonism -- his theogony (an account of the genesis of gods). It's already been hinted that he is much more anthropomorphic than Axial Age gods, but that will be explored in another post.