Here's the conclusion:
In the NT, the good news is always the proclamation of forgiveness of sin through the substitutionary death of Jesus, and the call to repent to believe in him. Sometimes that's all the NT mentions as the "good news"; sometimes it also seems to zoom out to include in the good news all the promises that flow to those who are so forgiven. What the NT never holds out as the gospel, however, is the bare declaration that the kingdom has come apart from the means of entering it (faith in Christ's substitutionary death). Speaking biblically, the gospel is either Cross or Cross-and-Kingdom. But it is never Kingdom alone.