According to LDS, what principles of the gospel were corrupted in the Great Apostasy?

In the LDS.org article on Apostasy , **the Great Apostasy** is described in the following terms: > After the deaths of the Savior and His Apostles, **men corrupted the principles of the gospel** and made unauthorized changes in Church organization and priesthood ordinances. Leaving aside the second part of the equation dealing with Church organization and priesthood ordinances, how exactly do Latter Day Saints believe the principles of the gospel were corrupted? **By way of background:** I've had a couple of conversations with LDS (current or former missionaries) over the last year or so, where they have sought to emphasize the broad agreement with essential beliefs with other Christians. I find it hard to reconcile this with the LDS doctrine about the Great Apostasy and am trying to understand what they really meant. Is a de-emphasis of fundamental soteriological differences recommended as part of engaging with other traditions, or is the view on the "Great Apostasy" that is not that significant with regard to an understanding of the fundamentals of soteriological doctrine?