Why would orthodox Christians consider Christian Science unorthodox if it essentially a mix of Augustine and healing? Why is Christian Science considered unorthodox? 


How is Mary Baker Eddy's neo-platonism different from Augustine's,
Aquinas', Calvin's, Jonathan Edwards', et. al.?
How is her understanding of the Incarnation different from
Scheiermacher's, Tillich's, Marcus Borg, et al?
How is her view of the sacraments different from the Quakers?


From what I can see, Mrs. Eddy puts together perfectly orthodox views on evil as privation, matter as shadows, and Jesus as Wayshower--just like Meister Eckhardt--and then applies these doctrines to Christian healing.  

If evil is a privation of good and has no real existence, isn't the best way to approach healing to see disease as a privation and not real? 

Maybe Jesus healed by removing the shadows which distort our vision of our true nature as God's children. If God is Spirit, and we are in His Image and Likeness, then doesn't it follow that we are spirit, and not matter? I'm not sure why Christian Science is a heretical cult since it is rooted in many purely orthodox strands of Christianity, albeit put together in an original, insightful way.  

Why, then, is Christian Science considered unorthodox if it has orthodox views?
This quote from catholic.com sums up why a Catholic group considers it unorthodox pretty well:


  Christian Science purports to be a Christian organization. It borrows
  heavily from the Christian vocabulary but denies all the fundamental
  Christian dogmas. It rejects the belief in a personal God, the
  Trinity, the divinity of Christ, the existence of sin and the devil,
  the Resurrection, and heaven and hell.


In short, Christian Science denies the fundamentals of the faith. This is how heresy is defined. It has nothing to do with having ideas similar to other Christian writers. 

Mary Baker Eddy (Catholic Answers)

Want more details? Mary Baker Eddy's full teachings are found in her book, now online, Science and Health, with Keys to the Scriptures. Here are several extracts with links. As you can see, Mary uses the same terms as the Bible does, but reinterprets them. 

25:3-9 tells us that Christ's blood did not cleanse us from sin on the cross:


  The efficacy of Jesus’ spiritual offering is infinitely greater than
  True flesh and bloodcan be expressed by our sense of human blood. The
  material blood of Jesus was no more efficacious to cleanse from sin
  when it was shed upon “the accursed tree,” than when it was flowing in
  his veins as he went daily about his Father’s business.


from http://www.christianscience.com/the-christian-science-pastor/science-and-health/chapter-ii-atonement-and-eucharist?citation=SH%2025:3-25:12

361:1-3 tells us that Christ is not really God Himself, but only an idea of God: 


  The Jew believes that the Messiah or Christ has not yet come; the
  Christian believes that Christ is God. Here Christian Science
  intervenes, explains these doctrinal points, cancels the disagreement,
  and settles the question. Christ, as the true spiritual idea, is the
  ideal of God now and forever, here and everywhere.


from http://www.christianscience.com/the-christian-science-pastor/science-and-health/chapter-xi-some-objections-answered

335:24-30 Tells us that sin and sickness are not real:


  XX. Mind is the divine Principle, Love, and can produce nothing unlike
  the eternal Father-Mother, God. The one divine Mind Reality is
  spiritual, harmonious, immutable, immortal, divine, eternal. Nothing
  unspiritual can be real, harmonious, or eternal. Sin, sickness, and
  mortality are the suppositional antipodes of Spirit, and must be
  contradictions of reality.


from http://www.christianscience.com/the-christian-science-pastor/science-and-health/chapter-x-science-of-being

30:3-12 tells us that Jesus and the Christ were separate entities. Also, He was a way-shower, and not the way Himself:


  Born of a woman, Jesus’ advent in the flesh partook partly of Mary’s
  earthly condition, although he was endowed with the Christ, the divine
  Spirit, without measure. This accounts for his struggles in Gethsemane
  and on Calvary, and this enabled him to be the mediator, or
  way-shower, between God and men. Had his origin and birth been wholly
  apart from mortal usage, Jesus would not have been appreciable to
  mortal mind as “the way.”


from http://www.christianscience.com/the-christian-science-pastor/science-and-health/chapter-ii-atonement-and-eucharist?citation=SH%2030:5-30:13