Oh Val, I have learned a lot over the years of reading their material and fellowshipping with them. Just like Baptists and Pentecostals, there is no "one size fits all". For example, you know that most Pentecostals are Trinitarian (believe that Father, Son, and Holy Spirit are three person but one God). But you do have the One-ness (or "Jesus Only") Pentecostals. Baptists are divided into numerous categories but you have Arminian, Calvinist and Liberal Baptists (some of them deny the deity of Christ).
Well, you have much of the same going on with the SDA. Some are Liberal and some are conservative. Some are legalistic and some are grace. Some believe the Trinity and others are close to being like Jehovah Witnesses in their theology.
Their main source of Bible interpretation is Ellen G. White. Some put her writings on the same level as inspired Scripture. Some of them refer to her writings as "the Spirit of Prophecy" (meaning that the Holy Spirit was speaking thru her). For some, this places her statements on a level of infallibility that cannot be questioned. Most of my friends in the SDA believe that her writings are only "commentary" though I have had some discussions with ONE people who wanted to convince me that her stuff is equal to Scripture.
Some are strict legalistic holiness, some are grace filled holiness (like most of us here), and some are loose liberals. Almost all of the ones I know believe that Jesus is the only way to salvation, but some add legalistic requirements such as Sabbath worship.
They ALL hold to the belief that Saturday is the day for church services (some believe that this is a requirement for heaven and others like the ones I consider friends balk at that idea though they still think Saturday is the most Scriptural day), soul-sleep after death and annihilation after resurrection for those who rejected Christ (one of those things I wish were true but my study of Scripture over the years as well as the numerous testimonies of those who visited Heaven and hell cannot allow me to accept that position), and strict vegetarianism.
Perhaps I can give a summation of what I have learned about my Baptists friends