Gopnik has a good article here about the history of Mormonism. I don't think it contains many surprises, but I just note these paragraphs about some of the religion's more curious ideas:
Smith held (especially in the sermons he preached toward the end of his life) that God and angels and men were all members of the same species. “God that sits enthroned is a man like one of you” and “God Himself was once as we are now, and is an exalted man” were two of his most emphatic aphorisms on the subject. (People who were “exalted,” in Smith’s language, were men moving toward godhood, as God himself had once been a man who achieved it.) Although in many other respects, as Fluhman and Bowman point out, Mormonism was orthodox in its outlook—Jesus is the sole Messiah, and his history as told in the Gospels is taken to be true, if incomplete—the doctrine of God-as-Man divided Smith’s cult from the others, and scared the pants off even charismatic Protestantism: the Protestants were willing to accept that we are made in his image, but not that we are made of the same flesh.
This doctrine led in turn to various theological niceties, which seem to have risen and receded in the faith’s theology over the years: one is that the birth of Jesus had to have been the consequence of a “natural action”—i.e., that God the Father knew Mary in a carnal way, in order to produce the Messiah. (This doctrine is currently in disfavor, but it had a long life.) Another is that God, being an exalted man, must have a wife, or several wives, as men do; she is known as the Heavenly Mother, and is a being distinct from Mary. (Smith’s belief in exaltation evolved into the belief that other planets were inhabited by men even more exalted than we are; Smith taught that the truly exalted will get not just entry into Heaven but a planet of their own to run. This is now taken, or taught, metaphorically, the way conventional Christians often think of Hell, but it was part of the story.)