I think perhaps the greatest abomination of the apostasy was the distortion of the duality of Jesus' nature - the denial that He was fully God but also fully human. "This is life eternal, that they might know thee, the only true God, and Jesus Christ, whom thou has sent," (John 17:3) goes way beyond knowing about Him, but it also does include knowing about Him.
My wife's favorite part of the Book of Mormon is 2 Nephi 4, specifically because it gives us a glimpse into the self-critical nature of a prophet that we rarely see. It makes Nephi more than a caricature; it makes him fully human. One of the things that makes Isaiah's description of the future Lord so compelling is that it shows His trials and pains and suffering; it makes Him more fully human. "Knowing" Jesus in this sense - allowing Him to be fully human in ALL ways except the actual commission of sin - opens up the possibility of such a deeper, more personal connection than knowing Him "only as God" ever can.
That's perhaps the biggest irony of the Restoration - that it emphasizes the way to have the deepest, most personal relationship with Jesus imaginable (ironically, outside of actual marriage) - that of "brother". Ideally, we know our siblings' faults and weaknesses but love them anyway. By removing all weaknesses and natural tendencies and temptations and spiritual growth, we literally create a chasm we can't cross - a creature we can't approximate - a Savior we can't truly know. Other religions preach the need for a personal relationship with deity, but they erase the principles that allow such a relationship actually to exist. There really is a chasm between their God and them, but it's a chasm of their own digging.