Joe Smith was a very imaginative writer, and he wrote the book of Mormon hoping to sell it. Many hundreds of other apocrypha, pseudepigrapha, Gnostic and other spurious writings have been written since 300B.C. Joe Smith simply is 'one of many' plagiarists before him. Most 'all' of these pseudepigrapha try to write in a style that copies and sounds like a biblical style and prose but most also rely heavily on plagiarizing the original scriptures for their own benefit and look of authenticity. Joe's work is like someone who put the bible in a mix-master with a few other documents, and his own imagination, and pushed the button. BOM verses contain lifted sayings of Jesus, Paul and Peter often in the 'same' sentence, strung together in completely different contexts and in a merry go round storyline. Joseph was also seriously involved with money digging, involving the use of peep stones and divination at the same time he put the BOM together, all these practices were highly condemned by God, and are seriously the antithesis of any of Gods revelation.
I will note that the OP is correct that the BOM is a very Christian sounding document, I would personally defend that the BOM is amazingly theologically sound as Joe had no intention of changing doctrines at that time. Joe changed his doctrines eventually, as in the coming of his King Follett sermon, and 'many' later 'revelations'. The Book of Commandments and subsequent additional teachings would add up to Mormonism having practically 'nothing' in common with Evangelical and Christian Theology. It is a great point in questioning Mormonism as to why practically none of their theology can be made to agree with the BOM.
Mormons themselves are generally 'wonderful' people, as their faith is a blend of Law keeping with a understanding of grace throughout. It creates a form of godliness, but is completely missing the True God and Savior / the truth of our sin / and with all the wild imaginations and teachings of Smith thrown in, it blinds Mormons to the true Scriptures, and misrepresents God and His Word as well... and that is just the beginning of Mormonisms errors...