As seems to be their frequent practice, the Desiring God site makes the John Piper book God is Gospel available as a pdf. Here is their summary of the book:
"Gospel" means good news - but what makes the good news good? What is the goal of the gospel, without which it is no longer good? It is that Christ's death brings sinners to God! Were it to bring us anywhere else we would be left hopeless. But the gospel is that God gives us himself - Christ died to give us Christ -, and this self-giving is his highest mercy to us and the best news for us! The most profound, most exceedingly gracious, final and decisive good of the good news is Christ himself as the glorious image of God revealed for our endless satisfaction.