What is God's good news before Jesus's death and resurrection? In Mark 1, we learn about both John's baptism of repentance and Jesus's proclamation that "the time has come.  Repent and believe in the good news!"

John's baptism


  And so John the Baptist appeared in the wilderness, preaching a
  baptism of repentance for the forgiveness of sins. 5 The whole Judean
  countryside and all the people of Jerusalem went out to him.
  Confessing their sins, they were baptized by him in the Jordan River.


Jesus's Proclamation


  14 After John was put in prison, Jesus went into Galilee, proclaiming
  the good news of God. 15 “The time has come,” he said. “The kingdom of
  God has come near. Repent and believe the good news!”


How would Jews have understood this at the time before Jesus's death?  It seems like the common understanding is that before His death and resurrection, the only sanctification for sin was through particular forms of sacrifice, based on this passage in Hebrews (NIV):


  22 In fact, the law requires that nearly everything be cleansed with
  blood, and without the shedding of blood there is no forgiveness.


So - other than that God being with us and loving us is clearly excellent news - how would this have been understood in Jesus's time before his death and resurrection?
The Good News is that the promised Messiah - God's annointed - has returned. The Kingdom of God was to be established.

When Jesus begins to preach in Luke 4, he overtly references himself as the promised Messiah of Isaiah.


  16 He went to Nazareth, where he had been brought up, and on the Sabbath day he went into the synagogue, as was his custom. He stood up to read, 17 and the scroll of the prophet Isaiah was handed to him. Unrolling it, he found the place where it is written:
  
  18 “The Spirit of the Lord is on me, 
     because he has anointed me 
     to proclaim good news to the poor. 
  He has sent me to proclaim freedom for the prisoners 
     and recovery of sight for the blind, 
  to set the oppressed free, 
     19 to proclaim the year of the Lord’s favor.”


The Kingdom would have had connotations of return to power and re-establishment of the "ancient order." The Kingdom announced in Isaiah 40 - 66 would have indicated a new social order, one in which there is equality and goodness of all, and that the throne of David would be re-established.

Luke in particular understood this reversal - the oppressed would no longer be on the bottom, the poor would be rich, etc... Look to Mary's Magnificat (Luke 1:48 - 52) to see this.

To many, the idea was conflated with political liberation from Rome, but the Good News preached was actually just the new social order of Isaiah 40 - 66.

What made Jesus' teaching unique was precisely the fact that Jesus redefined the notion of Messiah as applying personally and not just politically.