The Reformed as it is used today largely refers to Calvinists, although technically since Luther started the reformation, it should include Lutherans. The idea of the reformers was to Reform the Church and they threw out much of the Catholic idolatry and ritual salvation and switched it to faith alone.
Faith alone and James, we know why Luther was not a fan.
Type in "faith alone" to a bible search and only one phrase pops up:
James 2:17 Even so
faith, if it hath not works, is dead, being
alone.
Luther actually added the word ALONE to Romans 3:28. However if you decide to read the writings of Luther, you find that as the man who championed Faith alone, his faith alone included baptism for salvation and many other things today's "faith alone" crowd would be shocked by, and would be up in arms calling Luther a works salvationist. Lutherans have an interesting soteriology, they maintain baptism saves, while saying faith alone saves and works do not. It is confusing, but they get around it by saying baptism is a work of God, despite man performing it. (I am not a Lutheran, btw)
The reformation as you said calibob was not so much a return to Apostolic Christianity, but more of a return to Augustinian Christianity, since both Luther and Calvin were extremely influenced by Augustine, Calvin even admits it in his writings.