They are a QUASI/PSEUDO-CHRISTIAN CULT, "having a form of godliness dut denying its POWER."
They believe that on Oct. 22, 1844, Jesus entered the temple in heaven to both complete His atonement(Never mind the cross!) & to begin His "investigative judgment", a doctrine not found whatsoever in Scripture, an invention of Ellen G. White's.
They believe Ellen G. White was a great prophetess, altho she missed on quite a few prophecies. (A prophet of GOD'S was always 100% right!)
They believe the soul sleeps upon death. Jesus' telling the repentant thief on the cross, "Today, you shall be with Me in paradise" & His parable about the rich man & the beggar Lazarus prove this wrong.
EGW wrote,"Christ took upon His sinless nature our sinful nature. Christ took our nature and it's deteriorating condition." (Questions On Doctrine, PP. 654-656)
They believe God is finished with Israel, despite Scripture's saying differently, and God's miraculous restoration of the jewish nation.
They believe that Sunday worship is the mark of the beast, a false doctrine not even hinted at in Scripture.
While salvation is a "private" matter between Jesus and each individual, the SDA denomination is, at best, extremely heterodox, with much material ADDED to the commands & precepts God has given us thru His word.