They're vague in their Trinitarian/Christological formulations. For one they often believe that St. Michael the Archangel is the pre-incarnate Christ (like the Jehovah's Witnesses), although this may just be among the more traditional Adventists. They also use confusing language to describe the Incarnation itself... it doesn't seem like they know if they're Nestorian, Chalcedonian, Eutychian, or what. I suppose if you ignore their Christology, they do confess a Trinity but they seem to have a strange way of formulating it (undoubtably due to their previous non-Trinitarian stance early in the 20th century). Seventh-day Adventists are usually (always?) baptized upon entry into Orthodoxy, like Jehovah's Witnesses/Mormons.
Combine the above with Annihilationism (complete destruction of the wicked in lieu of the typical hell), Soul Sleep (people are effectively non-existent upon death, until resurrection), Investigative Judgment/Heavenly Sanctuary (their explanation as to why the prophecies of Christ's return in 1844 AD didn't seem to come to fruition; they say that Christ entered the "Heavenly Sanctuary" to begin the final phases of the "investigative judgment"), their end-times prophecies (persecution of non-Sunday worshipers and enforcement of Sunday worship, and huge emphasis on Bible prophecy interpretation), their view of themselves as the "Remnant Church" (or part of it, Saturday Sabbath worship being the mark of the remnants), extremely anti-Catholic views (Pope effectively anti-Christ, etc.), and so on and you have a fringe heretical cult pretending to be your next-door Evangelical church.
Effectively their entire church's theology presupposes the truth of post-"Enlightenment" anti-clerical/Catholic historical revisionism, which the very existence of Eastern churches proves to be a load of crock (they go along with the idea that a power-hungry Pope ruled the entire visible church with an iron fist from St. Constantine onward). And this is why EGW's works are complete bollocks.
