The great theologian D.A. Carson defines the gospel in this way: Thus the gospel is integrally tied to the Bible’s story-line. Indeed, it is incomprehensible without understanding that story-line. God is the sovereign, transcendent and personal God who has made the universe, including us, his image-bearers. Our misery lies in our rebellion, our alienation from God, which, despite his forbearance, attracts his implacable wrath. But God, precisely because love is of the very essence of his character, takes the initiative and prepared for the coming of his own Son by raising up a people who, by covenantal stipulations, temple worship, systems of sacrifice and of priesthood, by kings and by prophets, are taught something of what God is planning and what he expects. In the fullness of time his Son comes and takes on human nature. He comes not, in the first instance, to judge but to save: he dies the death of his people, rises from the grave and, in returning to his heavenly Father, bequeaths the Holy Spirit as the down payment and guarantee of the ultimate gift he has secured for them—an eternity of bliss in the presence of God himself, in a new heaven and a new earth, the home of righteousness. The only alternative is to be shut out from the presence of this God forever, in the torments of hell. What men and women must do, before it is too late, is repent and trust Christ; the alternative is to disobey the gospel (Romans 10:16; 2 Thessalonians 1:8; 1 Peter 4:17).
From here: http://s3.amazonaws.com/tgc-documents/carson/1996_biblical_gospel.pdf